─ did you play the piano today? ─ For five hours.
Newton was playing under an apple tree ____ an apple fell onto his head.
Which of the diagrams below shows the air temperature of Beijing in a year?
______ great scientist Qian Xuesen is!
I don’t know when he ______. When he ______, I will let you know.
------Whose shirt is this? ------ It _______ be Li Lei’s. It is too big for him.