A：用花粉离体培养获得的抗病植株，其细胞仍具有全能性
B：单倍体植株的细胞在有丝分裂后期，共含有20条染色体
C：植株X连续自交若干代，纯合抗病植株的比例逐代降低
D：放射性60Co诱发的基因突变，可以决定大豆的进化方向
用方框中所给单词的适当形式填空，使短文正确，通顺。（每词限用一次）
The population in China China has the____ population in the world, and about one ____ of the people in the world live in China. Because of the large____ , there is less____ space for each family. And it's difficult for lots of people____ jobs. The large population also causes many____ difficulties for the whole nation .For example, we're ____ of energy and water. Most cities are ____ than before, ____ the traffic is much heavier .The large population____ a serious problem.
我们常说“铁比木头重”是指铁的____ 比木头大，冬天里，户外装有水的水缸常会出现破裂是因为水缸里的水结成冰后，其体积____ （选填“变大”、“变小”或“不变”），密度____ （选填“变大”、“变小”或“不变”）．
人生的阴影，是自己遮挡阳光造成的。
计算：（﹣2）2+3﹣1﹣83
