应用DNA连接酶和限制性内切酶构建重组质粒，RNA聚合酶的功能是催化DNA转录为RNA，不用于重组质粒的构建；目的基因的检测应用质粒上的标记基因，目的基因的表达不一定能成功，有时还需要对目的基因进行修饰。

______and I'll get the work finished.
A. Having one more hour              B. One more hour
C. Given one more hour               D. If I have one more hour

Richard Gray was a famous explorer.He was also a millionaire.He had visited every country in the world.He had crossed the Antarctic,flown across the Atlantic by balloon,and climbed Mount Everest.Last year he decided to walk across Death Valley,the hottest place on Earth.He walked for days over the hot desert sand.One night he found the camp where he had been the night before.Gray had walked in a circle.He was lost.?

Two days later he had drunk all his water.He couldn’t walk.He crawled to the top of a sand dune,and there he saw a man.The man was wearing smart,clean trousers,a white shirt and a tie.Gray crawled over to him.?

“Water...water...”he said.?

“I’m terribly sorry,old boy,”replied the man,“but I haven’t got any water with me.”?

“Help me!”shouted Gary,“I’m a rich man...a millionaire... I’ll give you anything.”?

“That’s very nice of you,old boy,”said the man.“Look,I can’t give you any water,but would you like to buy my tie?”?

“A tie?Of course not!”screamed Gray,and crawled away.He crawled slowly up the next sand dune.His mouth was full of sand.His lips were cracked and dry.He couldn’t breathe.He reached the top of the dune and there he saw a huge good hotel.Girls were swimming in the large swimming pool.Beautiful fountains were all around the hotel.

“Is it a mirage?”he thought.“Am I dying?”He stood up and staggered down the dune.?

A waiter in a shining white uniform came out of the door.?

“Water...water...a bath! Food!”screamed Gray.?

“I’m sorry,you can’t come into this hotel,”said the waiter.?

“Why not?I’ve got plenty of money.I’m a millionaire.”?

“Ah,”replied the waiter,“but you aren’t wearing a tie,”?

1.The famous explorer ________.?

A.had crossed the Antarctic and the Atlantic by balloon?

B.had traveled all over the world?

C.had walked across Death Valley?

D.had ever been a millionaire?

2.Death Valley is ________.?

A.a valley where people may die from loss of ?

B.a dead place where people dare not go?

C.a terribly hot valley where people may die of heat?

D.a place’s name?

3.The man offered to sell his tie to Gray because ________.?

A.he wished to get some money from Gray?

B.Gray was a rich man?

C.he didn’t have any water with him?

D.he thought a millionaire needed to wear a tie?

4.If Gray ________,he would have got some water to drink in the hotel.?

A.had got a lot of money with him?

B.had put on his tie at once?

C.had said he was a famous millionaire?

D.had bought the tie from the man?

My mother is ill so I must go home and look _____ him.
  A. care of   B. after    C. for    D. on

----I still haven’t thanked Aunt Lucy for her present.

----It’s time you _____.

A. do　　　　　 B. did　　　　　 C. had　　　　 D. would

After eggs were found containing toxic chemical melamine（三聚氰胺） , the price of which is discounted ________ it was before.

A. half as many as　　　　　　　 B. as half as many

C. as half much as　 D. half as much as