What is the passage mainly about?

How the teeth of a zipper lock into each other as the slider passes. (The passage describes one tooth, then the slider, then what happens when it moves each way. All of it explains the locking.)

According to the passage, what is on the bottom of each tooth?

A small hollow. (The second paragraph gives both: the bump is on the top, the hollow is on the bottom.)

In this passage, a "wedge" is

a shape that pushes things apart as it moves between them (The last paragraph says the wedge slides between the rows and lifts them apart. That is what it does, so that is what it is.)

The last two sentences suggest that a zipper stays closed because

each tooth is held in place by the teeth beside it (The slider does no gripping, so it is not holding anything. The passage has already said the teeth beside a seated tooth hold it flat.)

How a Zipper Holds: Level 1 Reading Comprehension Questions

A zipper looks like one thing. It is really three: two rows of teeth, and a small slider that runs between them.

Look closely at a single tooth. On its top there is a little bump. On its bottom there is a small hollow. Every tooth is the same shape, and the two rows face each other.

Now the slider. Inside it, the path splits into a Y. When you pull the slider up, the two rows come in through the wide end and are forced together at an angle. The bump on one tooth drops into the hollow of the tooth opposite. Once it is seated, that tooth cannot lift out unless it is bent sideways again, and the teeth beside it hold it flat.

Pull the slider the other way and a small wedge inside it slides between the rows and lifts them apart. The slider does no gripping of its own. The teeth hold each other.

Comprehension questions