The lovers were meeting each other secretly, but their …… affair was soon known to everyone. A. clandestine B. covert C. unknown D. candid

The correct answer is A. clandestine.

Clandestine means done or occurring in secret, especially with a political or military purpose. In the context of the question, the lovers were meeting each other in secret, so their affair was clandestine.

The other options are not as accurate. Covert means kept secret or hidden, especially for political or military reasons. Unknown means not known or familiar to someone. Candid means open and honest, especially in speech or writing.