No one is allowed ____ the room in the daytime..
The secretary worked late into the night, ______ a long speech for the president.
There is no doubt _______ nearsightedness is a serious problem among the youth of our country.
You needn’t have ________ the speaker when he was speaking; there was enough time afterwards for you to ask questions.
It’s helpful to put students in a situation _______ they can learn how to cooperate with each other.
Lucy is a very optimistic girl. ______ she is faced with difficulties, she always sees the bright side.