6-21. prevent, prevents, to prevent, preventing, prevented.
[You prevent X.] = X is something that can or will happen if something does not cause it not to happen. But before it can happen, you do something to cause it not to happen. Because of what you do, X does not happen.
[I put the food inside the building to prevent animals eating it.]
6-22. fall, falls, to fall, falling, fell, fallen.
[X falls.] = X was more high before. But now X moves quickly down through the air. It moves down because there is not something touching X that prevents it moving down.
[Something fell from the top of this building.]
6-23. head, heads.
[X is your head.] = X is a round part of your body. Your mouth and eyes are parts of X. Something happens inside X when you think. Something inside X controls the other parts of your body.
[The animal moved its head down to drink some water near the ground.]
6-24. hit, hits, to hit, hitting.
[J hits K.] = J is moving quickly towards K before this moment when it touches K. Because it is moving quickly when it touches K, it can cause K to move or cause J or K to change shape.
[From the top of this big plant, something small and round fell down and hit my head.]
Lisa is holding something, because Lisa sees water falling down.
Lisa says: "__________."