In an appropriately designed experiment, a scientist is able to test the effect of:
a) a single variable
b) multiple variables
c) the hypothesis
d) scientific observations

In an appropriately designed experiment, a scientist is able to test the effect of A. a single variable.

In an experiment that's appropriately designed, there is typically one independent variable. The independent variable is the variable that one manipulates in an experiment.

In an appropriately designed experiment, a scientist is able to test the effect of a single variable. This allows the scientist to determine if the variable that is manipulated has an impact on the subject.

Read related link on:

link

A) a single variable

Explanation:

An appropriately designed experiment usually involves only one independent variable. This allows the scientist to truly determine whether the variable manipulated is what had an effect on the subject. You may test more than one variable, but this is usually done or experimented separately, or one at a time.

the answer to your question is b

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