Which of the following is an example of how a scientist might use a model?

1. A microscope is used to magnify a group of cells on a slide.
   
   
2. A stopwatch is used to time the rate of a chemical reaction.
   
   
3. A wrench is used to tighten a nut onto a piece of wood.
   
   
4. The end of a slinky is moved vertically up and down to simulate a wave.