The correct active sentence is option B, where "expecting the worst" is the subject that performs the action, reflecting an active voice in the sentence.
The revision of the passive sentence into an active sentence can be identified by the presence of a clear subject performing the action. Looking at the provided options, choice B is the active sentence as it has a clear subject "expecting the worst" performing the action of letting you "plan for trouble and avoid it." In contrast, the other options either retain some passive qualities or do not clearly present the action being performed by the subject.
The revised active sentence is option B: Pessimism is smart; expecting the worst lets you plan for trouble and avoid it.
When revising sentences to be active, it is important to identify the subject that is performing the action and ensure that this subject is clearly presented within the sentence's structure.