英语听力

The term biological clock is(36) to the means by which living things(37) their activity patterns, without any(38) cue, to the time of day, or the month, or the year. The biological clocks seem to be beautifully (39) to the needs of living things. They are (40) but little, if at all, by drugs, chemicals, or wide temperature difference-factors which may alter

substantially the rates of all ordinary (41) of the body.

The nature of the biological clocks’ mechanism is still a (42) . Two quite different theories can (43) for them. According to the first of these theories, (44) . This is believed to have evolved, aided by nature selection, as an adaptation to the rhythmic environment. It has

now become independent of environment. (45) the setting of their biological clocks, therefore, involves a constant adjustment to subtle

environment forces. But the search for the specific

timing system has been futile thus far. (46)