17题,我怎么觉着C和D都不对呢?tails有两种:(1)in the direction away from the sun(但是这种是less common kind)(2)get pushed back by the sunlight. 但是D却说always point in the direction away from the Sun啊?这个always就不对,而且只是说了第一种啊?? 到底D对不对呢?? 谢谢
第一段中确实提到了tails often steaming from it in the direction away form the Sun,但是这个tails是coma的啊?而题目中问的是tails of comets.我想这两种是不一样的吧?因为在最后一段中说到了comets和coma的关系。first the coma grows, then two distinct tails usuallly form.真不晓得他们到底是不是一回事呢。搞不懂.... 耷拉着耳朵的兔兔...
还有这一套的45题 我的答案给的是A. chemical structure of the pheromone is changed. 我的定位在这里:but some pheromones may convey different meanings and consequently result in different behavioral or physiological responses,depending on their concentration or when presented in combination.但是concentration and combination怎么是chemical structure 的变化呢?