Fill in the blank with the most appropriate word.
The computer ________ guaranteed by the company.

In this sentence, the subject "The computer" is singular, and therefore, the appropriate verb form to use is "is," which agrees with the singular subject.

Option B: are
This option is incorrect. "Are" is used with plural subjects, and it doesn't match the singular subject "The computer."

Option C: it's
This option is incorrect. "It's" is a contraction of "it is," and it doesn't fit grammatically in this context where a simple verb form is required.

Option D: aren't
This option is incorrect. "Aren't" is a contraction of "are not," and it is not appropriate for the sentence's singular subject and verb agreement.

The correct answer is Option A: is, which accurately matches the singular subject "The computer" and maintains proper verb agreement.