问题 多选题

下列关于植物双受精的说法中,正确的是(  )

A.双受精是指两个精子分别与两个卵细胞同时受精,形成两个受精卵

B.双受精是指两个精子分别与一个卵细胞和一个极核相融合的现象

C.双受精现象不是所有植物都具有的,而是绿色开花植物所特有的

D.双受精是指两个精子同时与一个卵细胞相融合,形成一个受精卵

答案

当花粉落到雌蕊的柱头上后,在柱头黏液的刺激下,花粉萌发出花粉管,花粉管穿过花柱到达子房胚珠珠孔后,前端破裂释放出两个精子,其中一个精子与珠孔附近的卵细胞融合,形成受精卵.另一个精子与中央极核融合形成受精极核.这个过程称为双受精.双受精现象是被子植物(又叫绿色开花植物)特有的受精方式.

故选:B、C

判断题
完形填空

第三节:完形填空(共20小题,每题1.5分, 满分30分)

Everybody gets unhappy. That’s why people eat a lot of  21  or spend lots of money on clothes—they think that these things will make them  22  !   23  , it is easy to create happiness, if you just have learned to be a  24  .

Giving  25  and resources to others who need them is a good thing to do. It will possibly contribute more to your happiness and to maintaining(保持) a   26   attitude than anything else. The key to successful family   27  is spending time staying with other family members. Give your time to your husband or wife,  28  time and resources to your children, and  29   they are the most valuable to you in the world.

Imagine this: a boy has  30  ,and you give him something of great  31  to him, such as by reading him a book. There is no  32  that you’ll see a big simile on his face. Maybe you’ll find that this is the happiest  33  of your life. You can also volunteer for a rescue service. There you will learn the meaning of“I cried  34  I had no shoes and then I saw a man who had no legs”.

Isn’t it true that the happiest people are typically those we consider foolish because they are  35  ready to give you the  36  off their back? It is also  37  that the most discontent(不满足的) people are the ones who are always making demands and never  38  others. Form the  39  of being a Big Giver, and then you will know one of the secrets to living a  40  and happy life.

21.A.junk food               B.meals                        C.fruits                        D.vegetables

22.A unhappy                 B.disappointed               C.happy                       D.satisfied

23.A.Mostly                   B.Actually                    C.Finally                      D.Naturally

24A.winner                    B.reminder                    C.receiver                    D.giver

25.A time                       B.money                      C.clothes                     D.food

26.A.positive

27.A.communication     B.negative

B.relationships       C.rude

C.hobbies       D.equal

D.topic

28.A. take                      B. bring                        C. devote                     D. lead

29.A.believe                   B.recognize                   C.understand                D.dream

30.A.something              B.nothing                      C.everything                 D.anything

31.A.value                     B.help                          C.use                           D.importance

32.A.wonder                  B.need                          C.doubt                        D.good

33.A.view                      B.person                       C.day                           D.moment

34.A.but                        B.because                      C.though                      D.if

35.A. never                    B.yet                            C.seldom                      D.always

36.A. clothes                  B. hat                           C. money                     D. life

37.A.true                       B.certain                       C.sure                          D.real

38.A.take in                   B.pay for                      C.care about                 D.worry about

39.A.culture                   B.custom                      C.look                         D.habit

40.A.healthy                   B.unforgettable              C.successful                  D.simple