直线切割法中，对岸救生岗位主责区1/3的水域为次责区。
参考答案：错
A．They are accurate and easy to pull.
B．Their shooting range is 40 yards.
C．They are usually used indoors.
D．They took 100 years to develop.
如图所示，A、B两个正点电荷相距2r，MN为其连线的中垂线，与连线交于O点，Q为MN上一点，且OQ=r，当A、B带电量相等时，测得Q点的电场强度大小为E，若将B的带电量加倍，电性不变，则Q点电场强度大小变为（ ）
A．2E B. C. D.
C.
D. 