题目内容：

Sweet peas, cucumbers, grapes ---- what do you think they have in common?

None of these vegetables grow on trees. They all don’t have strong roots, big trunks or long branches, which makes it harder for them to get sunlight. But don’t worry. They have developed their own unique way of growing taller climbing!

Take sweet peas as an example. The plant grows as a straight stem until it finds something to hold onto, either a nearby tree or a stick. That is when the stem makes small coil(卷曲) that helps the plant hold the stick tightly.

How these plants are able to do this has been a mystery to scientists for years. Even Charles Darwin was interested in this question. But it is not until now that a Harvard research team has finally found the answer. The study was published in the Journal Science earlier this month.

The key, as it turns out, is inside a kind of thread-like cell called “g-fiber cell”, which has the ability to shrink or stretch. Each stem of the pea plant is made of several layers of g-fibers. Once the plant finds something to hold onto, cells on side of the stem start to shrink, forcing the whole thing to bend and coil, which is a bit like how our muscles get our bodies to move.

What’s more, a pea’s coil is not exactly like that of a spring. If you look closely, you may find that a spring coils all in the same direction, but a plant’s coil is in two opposite directions, like a telephone line. This means that the stem can stay soft when pulled gently but become strong enough when pulled harder.

“You want the plant to have a little bit of flexibility(柔韧性) so that if the wind blows or an animal disturb it, it doesn’t break,” explained Sharon Gerbode, author of the study. “This structure allows the plant to easily accommodate small movement, but then if something really serious happens it can become strong and protect itself.”

1. According to the article, coiling happens in sweet peas plant to allow the plant to         .

A. form a straight stem

B. grow strong roots

C. develop g-fiber cells on the stems

D. climb itself up toward the sunlight

2.According to the article, which one is true about “a sweet pea’s coil”?

A. to be like that of a spring

B. to bend all in the same direction

C. to make the stem hard break

D. to make the stem get soft when pulled hard

3.When the sweet pea plant finds something to hold onto,           .

A. g-fiber cells on both sides of stem, forcing the stem to bend and coil

B. g-fiber cells on side of stem shrink, forcing the stem to bend and coil

C. g-fiber cells on the stem start to stretch, forcing the stem to bend and coil

D. there are more g-fiber cells on the stems

4.What’s the purpose of the writer in the passage?

A. To tell us why the sweet peas can climb the tree or stick.

B. To display new research allows scientists to understand more about climbing plants.

C. To show us new scientific research about the role of “g-fiber cell”.

D. To tell us the mysterious natural phenomena of some plants.