Idioms and Phrases - Verbal and Reasoning

In the following questions four alternatives are given for the idiom/phraseitalicised and underlinedin the sentence. Choose the alternative which best expresses the meaning of idiom/phrase.
Q1:

Despite the trust bestowed on the minister he turned out to be a snake in the grass during the revolution.

A a secret enemy

B a treacherous person

C an unforeseen danger

D an unexpected misfortune

ANS:A - a secret enemy

No answer description is available.