There ______ a book, two pens and three pencils on the desk.
By the first day of August, 2007, the PLA has its ______ birthday.
There is no doubt _______international cooperation is the key to dealing with cyber crime.
Listen ! Helen is singing in the next room.—It __________ be Helen. She is in Tianjin now.
Do you know whether scientists have ________a good way to deal with Influenza H7N9 or not?—Not yet .But they’re trying their best.