师傅带徒弟这种培训方式的开发主体是()。
A.师傅
B.徒弟
C.学校
D.企业或单位
参考答案:D
下列变化中,必须加入还原剂才能实现的是( )
A.MnO2→Mn2+
B.Zn→Zn2+
C.H2→H2O
D.CuO→CuCl2
Thanks to the heavy rain, the football match _____ until next week.
A.must put off
B.must have been put off
C.has to put off
D.has to be put off