Suppose you would like to find out which brand of glue holds better.
What variables would you need to control in
your experiment?

The amount of glue used, the material and how much of it you're using every time you test each glue, the temperature of the room, etc.

Explanation:

There are many answers to this question but think about the obvious ones first. Obviously you'll need to use the same amount of glue every time you're testing each type. The material used is also important and how much of the material you're using because different types of glue can work better with different materials, as well as how much material you're using. The temperature of the room can affect how well each glue holds up because often glue dries easier/quicker with heat, so in your experiment to make it fair you need to make sure that each glue is tested in the same environment.  

the answer is na (sodium)