问题
选择题
| It's good _____ old people to cross the road. |
A. help B. helps C. to help D. helping |
答案
答案：C
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| It's good _____ old people to cross the road. |
A. help B. helps C. to help D. helping |
答案：C
缺失
做基牙，设计隙卡，可摘义齿修复，戴牙半年后，
上卡环折断，造成该现象不可能的原因是（）