题干
_____ mobile phone is very convenient, school children are not allowed to own one.
A：If
B：While
C：Because
D：Whe
答案(点此获取答案解析）
B
，定义一种向量积：
＝(a1b1，a2b2)．已知点
，
＝，
＝，点Q在y＝f(x)的图象上运动，满足
＝
＋