A
作后置定语 " 以R 字母开头的词“我可不可以理解为 the word what is beginning with a letter "r" in the sentence is the word "robot" 然后就是把 what is 给省略了//不是what 是that(关系代词）that is beginning with a letter "r" in the sentence是定语从句因为分词短语也可以作定语， 所以也可以说beginning with a letter "r" in the sentence两者可互换