TO PICK
Alone the word usually means to collect fruit when it is detached from the branch or plant. Mushrooms, cherries, strawberries - they are all picked.

You can also pick a lock (if you are a thief and able to open a lock without the key...)

To choose. If you pick the right horse and put your money on it you can win. fortunately for the bookmakers, most people pick the wrong horses.

To eat off the bone. One shouldn't pick chicken bones in a restaurant, though it's quite nice to do so at home.

(The expression "To pick a bone with someone" means you want to talk over something in detail, the implication being that he is wrong and you are going to put him right.)

When a pickpocket steals your wallet he picks your pocket. Even though he might specialise in handbags and the like, he is still a pickpocket.

TO PICK UP
To collect or recover something or things which are lying on the ground, on the table...
To take something in your hand from wherever it is lying.

You also pick up the children from school when you take them home.
Or you can pick up a colleague on your way to work so that he doesn't have to use his car.

A pick-me-up, by the way is a quick drink intended to give you a little energy - even if it usually does the opposite.

TO PICK ON
To pick on someone is to attack them systematically and, by implication, unjustly. In nature, albino animals are often picked on by their fellows expelled or eventually killed.
It doesn't pay to be different...

In the exercise, type in the verb and preposition, in the correct tense.