He didn't answer the phone immediately as he was________ on a difficult math problem. A.busy to work...
2022-08-03 08:14:09 181次 上海民办新竹园中学2019-2020学年九年级上学期第二次月考英语试卷 单选题 反馈错误 加入收藏 正确率 : 100%
题目内容：
He didn't answer the phone immediately as he was________ on a difficult math problem.
A.busy to work B.busy with work C.busy working D.busying
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