已知马蛔虫体细胞内有2对染色体，下列图示能正确表达马蛔虫体细胞和生殖细胞中染色体组成的分别是（  ）

不等式组$\left\{\begin{array}{c}y\ge 0\\ y\ge x-2\\ y\le \sqrt{x}\end{array}\right.$所围成的封闭图形的面积为（　　）

    As darkness fell, hundreds of people in the Swiss village left their houses. They were staring（凝视）1at the mountain top in the distance. It was covered with 2 beautiful and dangerous.

    The huge mountain is called Matterhorn. Mountain climbers had 3the top, using the southern route. But no one had ever dared（敢）to try a winter climbing up the 4 side. But now one man was daring to try the 5route. He was Walter Bonatti, a great mountain climber from Italy.

    For two days he had climbed. The village people had watched him anxiously(焦急地). Now they were waiting to see his signal（信号）. If he planned to 6 the next day, he would light a green signal. A red light would mean that he was turning back.

    A tiny green light7 high on the mountain side. Bonatti was not giving up! The people8.

    The next day he continued his way upward. He was so lonely and so 9! But he would not give up. Again that night he lit the10 light.

    In the morning, Bonatti 11. He couldn't see the top, but he knew he was 12 there. Though the climb was painful, he moved up.

    Bonatti had spent months13 for the climb. Was the training enough? Did he have the strength and skill to climb to the top?

     He was finally at the top! News about his 14 was radioed to the world.

    The trip down the southern route was easy. He was warmly welcomed in the village. He had done the"15", and would be well remembered as a climber of all time.

已知$F_1,F_2$是椭圆$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1(a>b>0)$的两个焦点，以线段$F_1$$F_2$为边作正三角形$M{F}_1{F}_2$，若边M$F_1$的中点在椭圆上，则椭圆的离心率是(   )