Economics ____________ my least favorite subject at school.

In this sentence, 'Economics' is a singular subject, so it should be paired with a singular verb. 'Is' is the correct verb to use with a singular subject like 'Economics.' Therefore, the correct sentence is: 'Economics is my least favorite subject at school.' Choice A 'Am' is incorrect because it is a first-person singular form of the verb 'to be' and does not agree with the subject 'Economics.' Choice C 'Are' is incorrect as it is a plural verb form and does not match the singular subject 'Economics.' Choice D 'Been' is incorrect as it is a past participle and cannot be used as the main verb in this sentence structure.