因为able是形容词,to后面不能直接加形容词,需要加be组成不定式to be able ,表示能够……;she received 是massage的后置定语,其前省略了引导词that
固定用法:
be supposed to do sth 应该做某事
be able to do sth 能做某事
she received 是省略了引导词that/which 的定语从句修饰先行词messages.
Taylor was supposed to be able to learn from the messages she received.
泰勒应该能从她收到的信息中吸取教训。