In a controlled experiment there are many variables but there should only be 1 independent variable. This is the variable both a and c

that you record as data

that you change

that causes the change

both a and b

It is the variable that changes throughout the experiment.

Explanation:

Someone's age is an independent variable.

i have to report this, it doesn't relate to biology

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands