绿色开花植物花粉粒中的一个精子与卵细胞结合，另外一个精子与极核结合的过程叫做______．双受精这种受精方式是______所特有的．
绿色开花植物的花粉粒在柱头黏液的刺激下，萌发生出花粉管，花粉管穿过柱头、花柱，伸入子房，到达胚珠；花粉管的顶端破裂，两个精子移动出来，其中一个与卵细胞结合成受精卵，将来发育成种子的胚；另一个精子与极核结合成受精极核，将来发育成胚乳，双受精现象是绿色开花植物（被子植物）所特有的受精方式．
故答案为：双受精 绿色开花植物
| 阅读理解。 根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为 多余选项。 | |
| One of the favorite foods in the United States is the hamburger, a kind of flat round bread with fine-cut beef in between. 1 . At fast food restaurants, people order their food, wait a few minutes to get it over the counter, and carry it to their tables themselves. 2 .At some fast food restaurants , people can order their food, pay for it and pick it up without leaving their cars. 3 . Most of the restaurants sell hamburgers or other popular foods among Americans, In addition, there are many fast food restaurants that serve Chinese food, Italian food, chicken, seafood and ice-cream. The idea of a fast food restaurant is so popular that nearly every kind of food can be found in one. 4 . First , they are not formal restaurants. People wear any type of dress when they go to a fast food place. Second, they are fast. People who are busy do not want to spend time preparing their food or waiting while someone else prepares it. 5 . Finally , most food in a fast food restaurant is not expensive. Therefore, people can often eat at a fast food restaurant without spending too much money, while they may not be able to go to more expensive restaurants very often. | |
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