He has suspended his secretary on a flimsy ground.

vigorous
strong
sound
salutary

The correct answer is A. flimsy.

A flimsy ground is a weak or unconvincing reason for doing something. In this case, the man has suspended his secretary without good reason.

B. strong is the opposite of flimsy. It means something that is firm or sturdy.

C. sound is also the opposite of flimsy. It means something that is based on good evidence or reasoning.

D. salutary is a word that means beneficial or helpful. It does not make sense in this context.