静止站在水平地面上的同学对地面的压强最接近于( )
A:10 Pa
B:102 Pa
C:10 4 Pa
D:10 6 Pa
下面四个命题:①若直线a∥平面α,则α内任何直线都与a平行;②若直线a⊥平面α,则α内任何直线都与a垂直;③若平面α平面β,则β内任何直线都与α平行;④若平面α平面β,则β内任何直线都与α垂直。其中正确的两个命题是( )
四大洋中,没有我国河流注入的是( )
已知:Ⅰ.CR﹣39单体结构简式是:
Ⅱ.酯与醇有反应RCOOR′+R″OH →△催化剂 RCOOR″+R′OH(R、R′、R″代表烃基)
①—Is she seven?
—No, she isn't. She's eight.
②— Is she ten?
—Yes, she is.
③— Is she nine?
— Yes, she is.
④—Is she nine?
—No,she isn't. She's seven.
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