Let’s try doing the following experiment.
What to do：
Use string to hang a paper clip or other small object at about chest（胸部）level.
Pick up a stick，such as a broom handle. Take three or four steps away from the paper clip.
Now close one eye and walk toward the paper clip. Try to touch it with the tip of the stick. If you miss，try again，still keeping one eye closed. Now try it with both eyes open and see if it’s easier to do.
How it works：
In the experiment，you have to judge how far away the paper clip is. Your brain has several ways of doing this.
One simple way depends on how much your eye has to focus（聚焦）itself. Using only one eye，most people will find it difficult to touch the paper clip on the first try，but the brain still gets some information about distance—though not much.
Your brain can judge distance much better when you look at something with both eyes. In fact，your brain has more than one way to use both eyes in judging distance. For example，to see anything clearly，you have to make both of your eyes point at the object. When you look at a nearby object，your eyes turn inward. You can feel this happening if you look at the tip of your finger and move your finger toward your nose.
Your brain gets information from the eyes about how much they are pointing toward each other. Using that information，the brain can tell how far away any object is，whether it is a basketball or a paper clip.

How many materials do we need at least to do the experiment?

A．Two

B．Three

C．Four

D．Five

The passage is mainly about that with eyes our brain can judge         .

A．how big an object is

B．how high an object is

C．how far away an object is

D．how much information an object is

Which of the following is true according to the passage?

A．Our brain judges distance in one way when we use both eyes.

B．Our brain cannot judge the distance of a small object but a big one.

C．How much our eyes focus helps our brain judge the size of an object.

D．How much our eyes focus helps our brain judge the distance of an object.

From the experiment we can infer（推断）         .

A．with one eye we can see an object as clearly as we use two eyes

B．our eyes turn towards the inside when we look at an object very near

C．within 3 or 4 steps，the nearer an object is，the more clearly we can see it

D．our brain can hardly get any information about distance when we use one eye