It was presumptuous of him to make a remark in the assembly.

The correct answer is C. over-confident.

Presumptuous

means acting as if you have more right or importance than you really do. In this case, the person made a remark in the assembly without thinking about whether it was appropriate or not. This shows that they were over-confident in their own judgment.

A. ridiculous is incorrect because it means causing laughter or amusement because of absurdity. The person’s remark may have been inappropriate, but it is not necessarily ridiculous.

B. unthoughtful is incorrect because it means not showing or considering the feelings or wishes of others. The person may not have considered the feelings of others when they made their remark, but this does not mean that they were unthoughtful in general.

D. ambiguous is incorrect because it means open to more than one interpretation. The person’s remark may have been ambiguous, but this is not the main reason why it was presumptuous.