The man at the gate had a forbidding appearance.

Answer: Option B

Forbidding : unfriendly or threatening in appearance.
Lenient : (of a punishment or person in authority) more merciful or tolerant than expected.
Friendly : kind and pleasant.
Tranquil : free from disturbance; calm.
Mild : not severe, serious, or harsh.

Antonym of Forbidding is Friendly