But what we now know, is that for a number of diseases, there are defects in the system, where the body can't prune back extra blood vessels, or can't grow enough new ones in the right place at the right time.
但我们现在知道， 对一些疾病， 系统中存在缺陷， 在正确的时间和地点， 人体不能裁减多余的血管， 或是不能长出足够的新血管。