I'd say A: tidal waves. B, C, and D don't really seem to fit for me.
I think the respiratory system and circulatory system
Answer:
It would be D. Mitotic spindles form
Organism in an eniornment can compte for food
Explanation:
The experimenter alters the independent variable with the hopes of collecting data about how the dependent variable changes in response.Other variables have to be controlled so that any changes of the dependent variable are attributed to the known independent variable.