Context-based study：
Question: What is the writer or speaker trying to tell us?
Passage 1:
Garlic, a member of the lily family with its distinctive odor and taste, has been used throughout recorded history because it was considered to have beneficial properties. The earliest known record of its use is in Sanskrit records from 3,000 B.C.
 It was used as a medicine in Ancient Egypt, where it was used to cure 22 different ailments. It was also fed to the slaves who were building the pyramids because the Egyptians believed that, in addition to keeping the slaves healthy so that they could continue to work, garlic would make the slaves stronger so that they could work harder.
 The ancient Greeks and Romans found even more uses for garlic than the Egyptians had. In addition to using garlic to cure illnesses, as the Egyptians had, the Greeks and Romans believed that garlic had magical powers, that it could ward off evil spells and curses. Garlic was also fed to soldiers because it was believed to make men more courageous.
 Quite a few seafaring cultures have also used garlic because they believed that it was beneficial in helping sailors to endure long voyages. Homer used it on his odysseys, the Vikings always carried garlic on their long voyages in the northern seas, and Marco Polo left records showing that garlic was carried on his voyages to the Orient.
 Finally, even as late as early in the 20th century, it was believed that garlic could fight infections. Because of this belief, garlic juice was applied to soldiers’ wounds in World War I to keep infection at bay and to prevent gangrene.

Passage 2:
You may read all of this information about garlic, about how it was used in the past, and think that this was all just a lot of superstition, like breaking a mirror brings seven years of bad luck or throwing salt over your shoulder protects you from bad luck. But it is different. It’s not all just superstition, though some of it is. There’s actually a lot of scientific evidence that garlic does have certain medicinal benefits.
First of all, garlic does kill bacteria. In 1858, Louis Pasteur conducted some research that showed that garlic does actually kill bacteria. When garlic was used during World War I to prevent infection, there was good reason. There is actually research to back up garlic’s ability to kill bacteria. It’s raw, or uncooked, garlic that has this property. Raw garlic has been shown to kill 23 different kinds of bacteria.
Then, when garlic is heated, it’s been shown to have different medicinal properties. When it’s heated, garlic forms a compound that thins the blood. The blood-thinning property can help prevent arteries from clogging and reduce blood pressure, which may have some impact on preventing heart attacks and strokes.

Passage 3:
Many species of Asian bamboo have rather unique flowering and seeding cycles. What makes these cycles unique is that all the members of a species tend to flower and then seed at the same time; something else that is unique is that these simultaneous seeding cycles generally occur at rather lengthy intervals of perhaps 15 to 60 years or more. This means that a particular species of Asian bamboo may not flower and seed for many, many decades and then, when this species does flower and seed, all of its members tend to flower at the same time and then simultaneously set tremendous quantities of seeds before they die so that the seeds can grow into new plants.
One particular species of Chinese bamboo is a rather extreme example of the unique flowering and seeding cycles of Asian bamboo. This species tends to flower and seed less than once a century, and, when it does flower and seed, it does so throughout the world. This special Chinese species is known to have flowered and seeded in the early 1700s and in the mid 1800s and once again in the late 1960s. Its twentieth century flowering was quite well documented and showed how amazing the species’ flowering and seeding cycle is. Astoundingly, when this species of bamboo flowered and seeded in the late 1960s, it flowered and seeded in widely divergent areas; the flowering and seeding of this species of bamboo was noted in many parts of the world, including northern and southern Asia, North America, South America, and Europe.

Passage 4:
A particular problem that attracted a lot of attention in the second half of the twentieth century is how the survival of the giant panda is related to the unusual flowering and seeding cycle of Asian bamboo. The giant panda still lives in the wild in only a few mountain ranges in the southwestern part of China because its survival has been threatened both by hunters and by the destruction of the habitat it needs to survive.
What has been noted in the last few decades is that the panda’s survival is also threatened by the flowering and seeding cycles of the bamboo where the pandas live. Here’s what the problem is. Bamboo is the main source of food for giant panda. However, when there’s a massive flowering and seeding of the bamboo, the bamboo that has just seeded dies, and there’s a lag of quite a few years before the new young seedlings grow enough to provide food for the giant panda. When the bamboo dies, the giant panda needs to move to new areas to find food. The search for food has led the giant panda into areas that are more settled and more full of danger for the giant panda.