—He's friendly and helpful.
A:What's he like?
B:How's he?
C:What's he?
D:What does he like?
元素观是化学的重要观念之一。下列有关元素的说法错误的是( )
如图,∠ XOY=900,OW平分∠XOY,PA⊥OX,PB ⊥OY,PC⊥OW.若OA+ OB+OC=1,则OC=( ).