You can only be sure of _____ you have at present; you cannot be sure of something _____ you might get in the future.
On the celebration of the university’s 100th birthday, he said, “I have never experienced __________ time here as a graduate of Tsinghua University.”
Only when to explain thereasonfor this.
Large earthquakes __________ the ocean can create a series of huge, destructive waves called tsunamis that flood coasts for many miles.
He is so addicted to smoking that ________ seems to be no chance of talking him into quitting.
--- He is a very hard-working student. ---________.As far as I know, he often burns the midnight oil.