[文法]請問是省略介詞(in)嗎?

[motorolas (挑戰下一個階段)]

   I gained about three kilograms wirting the last book.

    請問動詞 write變成動名詞，因為介係詞in省略嗎?


   請高手指點

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→ SinclairH:分詞構句後，留下writing(主動)
→ motorolas:Thanks for your response.