根据题干要求填空 With a relative pronoun or a relative adverb: The ten-year-old American boy swam to and from a remote island within an hour,______was a great achievement for a kid of his age.
根据题干要求填空 With a relative pronoun or a relative adverb: The ten-year-old American boy swam to and from a remote island within an hour,______was a great achievement for a kid of his age. 【正确答案】：which
