管子表号sch40S中的S表示____。

The Browns _______ the trains; if not, they would have been at the get－together as sch

设有关系R和S，关系代数表达式R－（R－S)表示的是______。A．R∪SB．R∩SC．R－SD．R÷S

Theresa thinks that the present government is______.A．doing what they have promised to sch

The last paragraph is mainly concerned with______.A．the urgent need to add time to the sch

My sister used to study in a ______.A.girl schoolB.girls schoolC.girls schoolD.girls sch

UL-SCH用来传输____或____。