The student ______ for the final exam.

The correct answer is 'B: Was studying.' This choice correctly uses the past progressive tense 'was studying,' indicating that the student was engaged in studying for the final exam at a specific point in the past. Choices A, C, and D have errors in verb tense or structure, making them grammatically incorrect. 'Didn?ä?ü?óÔÇÜ?¼?óÔÇ×?ót study' (choice A) is in the simple past tense, 'Hardly studied' (choice C) uses an adverb modifying 'studied,' and 'Would have studied' (choice D) is in the conditional perfect tense, none of which are suitable for the context of the sentence.