Some colleges require that each potential student _complete_ an essay.
Here's why:
* Subjunctive mood is used to express wishes, possibilities, or hypothetical situations. It often follows verbs like "require," "suggest," "demand," and "insist."
* The original sentence uses the indicative mood, which simply states a fact.
* In the subjunctive mood, the verb "complete" changes to "complete" to reflect the hypothetical nature of the requirement.
The revised sentence now reads: "Some colleges require that each potential student *complete* an essay," implying that the completion of the essay is a requirement, not a certainty.