In the following question, some part of the sentence may have errors. Find out which part of the sentence has an error and select the appropriate option. If a sentence is free from error, select 'No Error'.
His assistance (1)/ wasn't happy (2)/ with his job. (3)/ No error (4)

The error lies in part (1) of the sentence. The noun 'assistance' means the act of helping or giving support, which is an abstract concept and cannot "be happy" or "have a job."
Instead, the person who helps (a human being) should be mentioned here. Therefore, the concrete noun 'assistant' must replace 'assistance' to make the sentence grammatically correct and meaningful.

Incorrect: His assistance wasn't happy with his job.

Correct: His assistant wasn't happy with his job.