The idiom Right-hand man means someone who is a trusted and highly reliable assistant or helper, who is often considered indispensable.
So,
The correct option is (B): Most efficient assistant
The CEO's sudden resignation threw the board into a tailspin.
What does the idiom "threw into a tailspin" mean?
The politician's vague answers clearly showed he was just beating around the bush.
What does "beating around the bush" imply?