This question is incomplete as it lacks options, the options are:
A) a single variable
B) multiple variables
C) the hypothesis
D) scientific observations
The answer is A
Explanation:
An experiment is conducted to solve a particular problem or find answers to a given scientific question. In an experiment, which usually consists of variables, only A SINGLE VARIABLE is tested at once.
This means that the effect of a variable called INDEPENDENT VARIABLE is tested at a time. The independent variable is the variable that is changed or manipulated in an experiment. This means that only a SINGLE VARIABLE can be changed at at time in an an appropriate design experiment.
