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.
which
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.
which
