“If you run for more than five minutes at any time, you might need a pair of running shoes,” advises Stephen Pribut, a US sports medicine expert. Running shoes are highly technical footwear. They provide stability（牢固）while bearing up to three times the wearer’s body weight. But it’s not easy to find the right pair. Finding the right running shoes is something of an art, or a science and a feel.
The science part begins with the shape of the arch（弓）of your foot, which anyone can find out at home with this quick experiment: Put your foot in water and place it on a piece of brown paper. If you see a “C” shape on the paper when you remove your foot, you have a rare high arch. If the shape looks more like a rectangle, that means you have flat feet. See something in between? That’s a normal arch.
Conveniently for shoppers, shoe companies nowadays divide their shoes in three categories: neutral(for high arches), stability(for normal or low arches) and motion control(for flat arches). So you will know which type suits you.
At this point, most people would just grab an appealing shoe and try it on. But professionals would do a few quality-control tests. First, you bend the shoe toe to heel to see where it bends. If it’s not at the forefoot---where the foot actually bends, be afraid. Then you grip both ends and twist in opposite directions. If you can twist it like a towel, it means there’s zero support. Finally, you squeeze(挤)the heel in both directions. A stable heel won’t cave in.
Now you need to check the mold(模子)that shapes the inside of the shoe: whether it’s wide or narrow in the mid-foot, how it sits on the heel and how roomy the toe box is.
It’s wise to hold off until the afternoon to make the shoe purchase, to allow for any swelling(肿胀) that your feet do throughout the day. Toes also decide sizing choice. The rule is you need a finger’s width from your longest toe (whether that’s your big one or not) to the end of the shoe.
What is the main idea of this passage?

A．Advantages of wearing running shoes fitting you.

B．Ways to get to know about the shape of the arch of your foot.

C．Advice on how to choose the right pair of running shoes.

D．Best time to buy a pair of running shoes.

If the arch of your foot looks like a “C” shape, you have _________.

A．a normal arch

B．a high arch

C．a flat arch

D．a low arch

．The underlined phrase “cave in” most probably means ______.

A．bend

B．stretch

C．shake

D．crash

．Why is the late afternoon the ideal time to go shopping for shoes?

A．We are likely to be more patient in the afternoon.

B．Feet usually become large late in the day.

C．The toes become longer late in the day.

D．The arch of our feet will be in best shape in the afternoon.