(1)是省略了。补充完的是:but he is hardworking(2)not only…but…as well这个句型与not only…but also…含义相同,只是结构上的差异而已。其实不存在not only but as well的结构,是not only but also,省略了also,然后在句末加上as well来加强语气。as well也可以省略。(3)当然是a句对。not only---but also----,but与also不分开,只是also能省略
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