He has tried twice, and he is asked to have_____third try.

A.try

B.tried

C.has

D.had

A.infuse

B.fill

A、have tried

B、have been tried

C、has tried

D、has been tried

A.say

B.will say

C.said

D.would say

e problem.One of these，for example，was the great Italian artist, Leonardo da Vinci(达·芬奇).In the sixteenth century he made designs for machines that would fly.But they were never built.Throughout history, other less famous men have wanted to fly.An example was a man in England 800 years ago.He made a pair of wings from chicken feathers.Then he fixed them to his body and jumped into the air from a tall building.He did not fly very far.Instead，he fell to the ground and broke every bone in his body.

The first real steps took place in France, in 1783.Two brothers, the Montgolfiers, made a very large “hot air balloon”.They knew that hot air rises.Why not fill a balloon with it？The balloon was made of cloth and paper.In September of that year，the King and Queen of France came to see the balloon.They watched it carry the very first air passengers into the sky.The passengers were a sheep and a chicken.We do not know how they felt about the trip.But we do know that the trip lasted eight minutes and that the animals landed safely.Two months later，two men did the same thing.They rose above Paris in a balloon of the same kind.Their trip lasted twenty-five minutes and they travelled about eight kilometers.

26.Leonardo da Vinci ______ .

A.said that man would fly in the sky one day

B.built a kind of machine which never flew

C.drew many beautiful pictures of birds

D.made designs for flying machine

27.Eight hundred years ago an Englishman ______ .

A.made a kind of flying machine

B.tried to fly with wings made of chicken feather

C.wanted to build a kind of balloon

D.tried to fly on a large bird

28.In fact，the Englishman who tried to fly ______ .

A.lost his life

B.flew only 8minutes

C.got badly wounded

D.succeeded in flying

29.The very first air passengers in the balloon were ______.

A.two animals

B.two Frenchmen

C.the King and the Queen

D.the Montgolfiers

30.When did two Frenchmen rise above Paris？______

A.In December 1783.

B.In September 1783.

C.In November 1783.

D.In the seventeenth century.

A.simple sentence

B.compound sentence

C.complex sentence

D.compound-complex sentence

A.took off

B.tried on

C.put away

D.hung up

A.many improvements

B.little improvement

C.few improvements

D.a little improvement

画出下述两种商品个人偏好的无差异曲线:汉堡包和软饮料。指出个人满足[或效用)增加的方向:（1)乔

画出下述两种商品个人偏好的无差异曲线:汉堡包和软饮料。指出个人满足[或效用)增加的方向:

(1)乔的无差异曲线为凸的，不喜欢汉堡包和软饮料。

(2)简喜欢汉堡包，但不喜欢软饮料。如果服务员给她一杯软饮料，她会不喝倒掉。

(3)鲍勃喜欢汉堡包,但不喜欢软饮料。但是如果服务员给他一杯软饮料，为了礼貌他会喝掉。

(4)莫利喜欢汉堡包和软饮料,但坚持精确地按照两个汉堡包搭配一杯软饮料来吃。

(5)比尔喜欢汉堡包，但对软饮料无所谓喜欢或不喜欢。

(6)玛丽从额外一个汉堡包中获得的满足是从额外一杯软饮料中获得的满足的两倍。

Draw indifference curves that represent the following individuals ’preferences for hamburgers and soft drinks. Indicate the direction in which the individuals' satisfaction (or utility) is increasing.

a. Joe has convex indifference curves and dislikes both hamburgers and soft drinks

b. Jane loves hamburgers and dislikes soft drinks. If she is served a soft drink, she will pour it

down the drain rather than drink iT.

c. Bob loves hamburgers and dislikes soft drinks. If he is served a soft drink, he will drink it to be polite.

d. Molly loves hamburgers and soft drinks, but insists on consuming exactly one soft drink for every two hamburgers that she eats.

e. Bill likes hamburgers, but neither likes nor dislikes soft drinks.

f. Mary always gets twice as much satisfaction from an extra hamburger as she does from an extra soft drink.

t, and she didn't tell him. She didn't tell him, and, you know, she was petrified that he's gonna find out what she did, and then he's not gonna want her, and he's not gonna want the baby ... She got so wrecked about it that she burned thousands of dollars worth of paychecks. Who does that？ And I tried to get her to just relax and to think about the publicity, or think about an abortion, or think about, you know, her word. "Just keep your word."

A.he had

B.had he

C.he has

D.has he