根据08prep的讲解：
现在分词在句尾用逗号隔开，必须要注意的一点是这个结构从来都没有失去过“做定语”的功能，只是优先做状语而已，即优先修饰到前面主句的主语和谓语。但如果前面主句的谓语是完成时态，那么既然已经完成了，分词就无法再做其的伴随，所以只剩下做定语的功能。具体例子，楼主可以参考新prep第一部分的188题的DE项。
（Neuroscientists, having amassed a wealth of knowledge over the past twenty years about the brain and its development from birth to adulthood, are now） drawing solid conclusions about how the human brain grows and how babies acquire language.
A. Neuroscientists, having amassed a wealth of knowledge over the past twenty years about the brain and its development from birth to adulthood, are（正确答案）
B. Neuroscientists, having amassed a wealth of knowledge about the brain and its development from birth to adulthood over the past twenty years, and are
C. Neuroscientists amassing a wealth of knowledge about the brain and its development from birth to adulthood over the past twenty years, and are
D. Neuroscientists have amassed a wealth of knowledge over the past twenty years about the brain and its development from birth to adulthood,
E. Neuroscientists have amassed, over the past twenty years, a wealth of knowledge about the brain and its development from birth to adulthood,
