Clothing made of man-made fibers has certain advantages over ______ made of natural fibers like cotton，wool or silk.

The Three Gorges will offer you a wonderful trip, ______ you’ll remember all your life.

.Among all the problems,_______is so difficult as this one. 

If I could help___,I needn’t have taken trouble to send the broken computer to the repairing centre.

Understanding the cultural habits of another nation,especially ______containing as many different subcultures as the United States,is a complex task.