回柱放顶前注意哪些事项?
参考答案:
(1)必须对放顶安全工作全面检查,清理好退路;
(2)必须指定有经验的人观察顶板。
The project alongside with the experiment we had once devoted so much time__________ perfectly.
A.to work out
B.to working out
C.to worked out
D.has worked out
汉字国标码GB 2312-80把汉字分成
A.简化字和繁体字2个等级
B.一级汉字、二级汉字和三级汉字3个等级
C.一级常用汉字、二级次常用汉字2个等级
D.常用字、次常用字、罕见字3个等级