Before a problem can be solved, it must be obvious ________the problem itself is.(2011·湖南)
The train ________ arrive at 11∶30, but was an hour late.
.The two ladies are ________ the same age, but there seems to be ten years ________ them.
Paper produced every year is ________ the world's production of vehicles.
We have done things we ought not to have done and ______ undone things we ought to have done.
— Why weren't you at the meeting?— I ________ for a long distance call from my sister in America.