有人在某与世隔绝的小岛上引入20只某种高等动物，尝试在该生态系统中增加新的种群，其中有两只动物带有常染色体隐性基因a，该基因的纯合体在胚胎早期致死。下列关于该种群变化趋势的叙述，正确的是[ ]
A．该种群数量变化始终符合“J”型增长曲线
B．基因a频率逐渐降低，很快消失
C．Aa的基因型频率逐渐降低
D．增加新种群必然导致该生态系统组成成分的增加
答案：C
| 完形填空。 | ||||
| Mr. Green heard that a certain government department (政府部门) wanted a clerk (职员), 1 he wrote and 2 the position (职位). But while he was waiting for 3 , a friend of his introduced him to the head of the department. And the head at once gave him 4 . Several months 5 , 6 Mr. Green was working in the department, he got a letter from his old address. This letter said: "Dear Sir, We are 7 to have to tell you that we cannot offer you the work in this department because we do not think that you would 8 do the job successfully." Mr. Green laughed, but when he looked at the letter more 9 he was 10 to see that he signed it himself! | ||||
|