先不管逻辑语意应该怎样,serving是伴随前面动作的,但是前面有两个动作,rises and falls,那么到底是rise还是fall还是两个动作同时伴随有serving这个动作呢?而且把can改成possibly改变句意,愿意是说can可以,改了之后变成也许可以,显然不行。。再者approximate: 近似,大约,和possibly有语意上的重复。。最后根据语意理解,是说这个根据温度变化的number可以当成近似温度计,那么serve这个动作应该是the number发出的,而不应该是伴随rise和fall发生的
remember that PRONOUN AMBIGUITY IS NOT AN ABSOLUTE RULE.
in general, eliminating on pronoun ambiguity is not a reliable thing to do, unless the ambiguous pronoun is specifically contrasted against a SPECIFIC NOUN in other choices. for instance, if you saw a split between "it" and "that number", then you could safely choose the latter. however, you should not generally eliminate choices just because they have ambiguous pronouns.
we have seen way too many correct answers with ambiguous pronouns to advise this sort of elimination anymore.