It's not fair to leave dogs loose.

Answer: Option B

Loose : not firmly or tightly fixed in place; detached or able to be detached.
Closed : not open.
Chained : fasten or secure with a chain.
Tight : fixed, fastened, or closed firmly; hard to move, undo, or open.
Locked : fastened or secured with a lock.

Antonym of Loose is Chained