A:NH4+、NO3-、CO32-、Na+
B:Na+、Ba2+、Cl-、SO42-
C:NO3-、K+、Cl-、Na+、OH-
D:AlO2-、K+、OH-、Al3+
① AB→−AC→=BC→ ;
② AB→+BC→+CA→=0→ ;
③若 (AB→+AC→)·(AB→-AC→)=0 ,则△ABC为等腰三角形;
④若 AC→·AB→>0 ,则△ABC为锐角三角形.
上述命题正确的是( )
Dear Jenny,
Now we are in the hospital of our city . My mother and I have a bad cold . We sees many children here . Some people have a cold. Some people have a headache. Some people have a fever. They a re waiting outside the doctor's room .Now it's our turn.
Yours,
Jack
下列说法正确的是( )