While playing ping-pong, our eyes see the ball coming, judge its speed and then hit it back ________ it should go. 

The summer holidays are not far away _________ we can stay at home and read some good books.

I can't figure out ________ it is that makes him so difficult at school.

The people, ________ had been damaged by the flood, were given help by the Red Cross. 

“All     is necessary for the triumph of the evil is     good men do nothing．” Edmund Burke said．