Which statement describés an experimental procedure that is properly controlled?

A. A survey shows the 10 best action movies made in the past five
years.

B. Twenty mice are fed a diet high in protein and their weights are
measured every day for six weeks.

C. Fifteen tomato plants are given 5 mL of a saltwater solution every
day, another 15 tomato plants are given 5 mL of plain water, and
each plant's growth is measured each week.

D. One hundred watermelon seeds are planted in full sunlight, while
100 pumpkin seeds are planted in partial sunlight.