The company identified nine new postures we had never seen before, all of which are driven by this new breed of devices.我知道all of which(非限制性定語從句)不能改成all of them,但不知原因。若非要改成all of them的話,好像就要把逗號改為分號,或者在逗號后加連詞and,再或者是逗號改為句號。這樣認為正確嗎? 連詞和標點符號怎么用?尤其是逗號,分號,句號和連詞。請老師一定為學生解惑,謝謝您。