Before joining the Department of Defense, Mr. Panetta _______ as director of the CIA from February 2009 to June 2011.
Who is it up ____ decide whether to go or not?
Wang Mei is one of many Chinese teenagers _____ “on the go”
The two boys fought and fought until one ______.
He will _____ our class to sing at the school singing contest.
They told us that these small apples are often sweeter than big ____.