Final answer:
Option B changes the original sentence to active voice by stating that 'Scientists reached a decision about when to begin the experiment,' making scientists the doer of the action.
Step-by-step explanation:
The revision that changes the sentence to use the active voice is option B) Scientists reached a decision about when to begin the experiment. In this revised sentence, "scientists" are the subject performing the action, "reached," which aligns with the concept of active voice.
The original sentence was in passive voice because the subject, "a decision," was the recipient of the action and "by scientists" indicates who performed the action. By revising sentences to feature the doer (the subject) actively performing the action rather than being acted upon, the writing becomes clearer and more engaging for the reader.