题目

某电场的电场线如图所示，质子在A、B两点受到电场力的大小分别为FA和F B，则它们的关系是A．FA=FB           B．FA<FB     C．FA>FB           D．无法比较 答案：C19．How often does Mr．Green go to see his parents？A．Twice a week．   B．Tree times a year．   C．Twice a month．