His smooth manners endeared him to everyone.

A. hard

B. rough

C. gruff

D. tough

Answer: Option B

Solution(By Examveda Team)

Smooth : having an even and regular surface; free from perceptible projections, lumps, or indentations.
Hard : solid, firm, and rigid; not easily broken, bent, or pierced.
Rough : having an uneven or irregular surface; not smooth or level.
Flat : having a level surface; without raised areas or indentations.
Tough : (of a substance or object) strong enough to withstand adverse conditions or rough handling.

Antonym of Smooth is Rough