Liu Xiang had worked hard . ________， he won the first prize in the 28th Olympic Games.

Sometimes drivers give him a tip, so that he has just enough money to _____.

--- How do you find Mr Li’s lecture? --- Good indeed. It_______ many problems we have come across in our study.

The number of the students in our class __________ to 54.

People have planted a great many trees in order to ____wind and sand in the desert.