You can cross the street when you see___________.

In the global economy, a new drug for cancer, itis discovered, will create many economic possibilities around the world.

That must be Mr. John.—No, it ________ be him. I saw him off at the airport half an hour ago.

It was on a train _____ I was travlling to Xi’an _____I made the acquaintance of the old professor from UK

The child said that he had _____ the pen on the desk, but I thought he ____ to me