The official ________ to say more about the plan, so the details of it remain secret.

One way for students to prevent H7N9 flu virus is to open the windows of the classroom to allow the air to ________.

 I can't say which wine is best---it's a(n)_______of personal taste.

—Will you be ______ this evening, Mary?—That depends. I am afraid I will be with my manager discussing a plan.

The young couple have been looking for houses，but haven’t yet found _________they can afford．