People in the West celebrate Christmas _______ each other presents.

Some researchers believe that there is no doubt____a cure for AIDS will be found.[ ]

Better not to ignore the past but learn from it instead. _____, history has a way of repeating itself.

(2013 ·吉林长春三校高三调研) Though you’ve got a tight schedule these days, I should be ________ if you could spare time to attend our meeting today.

You’d better wear your coat, ______ you will catch a cold.