放渣过程中发现渣中带铁较多时应勤堵、勤放，防止灼坏小套。
参考答案：对
He looked as if he ______ the answer. [ ]
A. knew
B. had known
C. knows
D. has known
国家对导游人员实行计分管理，导游人员计分办法实行年度多少分制？
