Final answer:
The English grammar question involves a sentence completion task. The correct word to fill in the blank in the given sentence is 'was'. An understanding of subject-verb agreement rules is necessary to answer such questions.
Step-by-step explanation:
The question pertains to an English grammar exercise. In the provided sentence, the correct word to fill in the blank is 'was'. The sentence should be written as: 'Significant time and effort was spent on perfecting her cover letter'. The verb 'was' is used because the subject 'significant time and effort' is considered singular, hence requiring a singular verb.
Learn more about Subject-verb agreement