At one's wit's end

Answer: Option B

Explanation:

Example : By taking side of the culprit he dug the grave of his reputation.

Answer: Option C

Explanation:

Example : He is such a great spokesperson, whenever he takes the floor there is a pin drop silence.

Answer: Option C

Explanation:

Prejudice means Preconceived opinion not based on reason or experience.

Example : You must not evaluate anything with a jaundiced eye.

Answer: Option A

Explanation:

Example : He always use to throw cold water on my plans.

Answer: Option C

Explanation:

Example : The rivals always flog a dead horse to insult their enemies.