英国某地的桦尺蠖多为灰色,生活在长满灰色地衣的树干表面,但也有个别突变型为黑色桦尺蠖。19世纪中叶后,工业污染导致该地区的树干变黑,黑色桦尺蠖的数量迅速增加。请回答:(1)黑色桦尺蠖和灰色桦尺蠖_______(填“是”或“不是”)同一物种,因为它们彼此间不存在_______隔离。(2)在不同环境下,两种桦尺蠖数量差异是___________的结果。(3)桦尺蠖的体色是由一对等位基因决定的,当环境逐渐受到保护,树干上的灰色地衣恢复生长后,13、The more ________ you listen to the tape, the
________ you will find it to understand.
A. carefully; more
easily
B. careful; more easily
C. carefully;
easier
D. careful; easier