氯气瓶瓶阀和易熔塞上紧后，螺扣外露不足三扣时，（）。
A、不影响充装
B、加力拧紧直至超过三扣
C、不能充装
D、降低充装压力
参考答案：C
―I called you this morning, but nobody answered.
―I ______ the flowers in my garden at that time.[ ]
A. watered
B. was watering
C. water
什么叫跨步电压？其大小与什么有关？
