Biology

The correct answer is repeat.

The sentence should read:

"Scientists repeat experiments to make sure the results are meaningful."

Explanation of the options:

A.perform  

While scientists do perform experiments, the word "perform" only refers to the action of conducting the experiment. It doesn't imply that the experiment is repeated to ensure its reliability or validity. The focus here is on ensuring that the results are meaningful, which typically involves repeating the experiment to verify the results.

B.repeat  

Repeat is the best choice because scientists often repeat experiments to confirm the reliability of the results. Repetition is a key metho...