December 17, 2011 was a sad day for the North Koreans, ______ their top leader Kim Jung-ill passed away unexpectedly.

It’s impossible for ____ few people to finish ____ a lot of work in only two days. 

You must turn off the gas after cooking. You can never be ______ careful withthat.

 He often keeps English _______ ___________,

Faced with the exams, we should work as hard as we can.       , we shouldn’t do it at the cost of our health.