C:CH4、C4H8
A:C2H4、C3H8
B:CH4、C5H8
D:C2H6、C3H8
生活中处处有化学,请用所学知识回答下列问题:
—Will there be schools in the future?
—No, there______.
设x,y∈R,向量a→=(x,1),b→=(1,y),c→=(2,-4)且a→⊥c→,b→//c→,则|a→+b→|( )