Do you have any idea ______ on earth has happened to our friend?

Is your father a Party member ? – Yes, he the Party three years ago. He a Party member for three years .

What will you do if it _____ tomorrow?

A train is going _____ a tunnel. [ ]

I met Daniel in the street yesterday, I ________ him since he left for Beijing.— Well, does he look like what he used to be?