Here's a problem to solve: 22 Sandy is conducting an investigation to find out which food his dog likes best. Which is the manipulated variable in his investigation?

Among the 4 following options, which is the correct answer?

- A: The color of his dog's food dish
 
- B: The kind of food he gives his dog
 
- C: The amount of food he gives his dog
 
- D: The time of day he feeds his dog
 