大全请教~谢谢~

大宝店小二

As part of their therapy, young polio victims learning to live with their disabilities were helped to practice falling during the 1950s, so that they could learn to fall without being hurt.
(A) As part of their therapy, young polio victims learning to live with their disabilities were helped to practice falling during the 1950s
(B) As part of their therapy, young polio victims learning to live during the 1950s with their disabilities were helped to practice falling
(C) Young polio victims learning to live during the 1950s with their disabilities were helped to practice falling as part of their therapy
(D) Young polio victims learning to live with their disabilities were helped to practice falling during the 1950s as part of their therapy
(E) During the 1950s, as part of their therapy, young polio victims learning to live with their disabilities were helped to practice falling

请问为什么E是正确答案？young polio wictims能够做part of their therapy的动作发出者吗？还是as引导的成分仅仅只是作为插入语?
谢谢！