The correct answers are The promotion came completely out of the blue. and I was under the impression that he was quitting!

Many idioms rely on the definite article "the" to sound natural.

• "Out of the blue" means unexpectedly. Omitting the article ("out of blue") is incorrect.

• "Under the impression" means believing something to be true.

• "On the whole" means generally or mostly. Using "a" instead of "the" ("on a whole") is a very common mistake!