Which of the following is a distinguishing feature of a controlled experiment?
AOnly one variable is changed at a time.
BAll variables are changed simultaneously.
CNo variables are measured.
DThe results are predicted before starting.
Explanation
📌 A controlled experiment changes ONE variable (the independent variable) while holding all others constant. This isolates the cause of any observed effect. Distractor B destroys causal reasoning; C omits measurement entirely; D describes hypothesis-only work, not experimentation.