The exercise is so difficult that it is ________ the abilities of most of the class.
There is _________ that her daughter will pass the exam to go abroad to study.
The key _________ the string was put into the door to stop the kite _________.
_________ that he had fallen behind,he tried to work harder.
Plastic and rubber won't _________ electricity,but copper will.
____no need for us to discuss the problem again since it has already been solved.