题干
_______, I suppose, and the housing problems for about 280,000 low-income families in this area could be settled.
A：If you double your effort
B：So long as you keep your spirits
C：A bit more efforts
D：Making greater effort
答案(点此获取答案解析）
C
，向量b=
，则|2a－b|的最大值是（ ）
