单项选择题A2 题型 30岁女,宫内孕第二胎,妊娠合并糖尿病,无关的因素是 A、羊水过多 B、巨大胎儿 C、受孕率降低 D、真菌性阴道炎 E、妊娠呕吐
单项选择题As shown in Figure, there are three point charges in the space, , , and . S is a closed surface. The permittivity of vacuum is . The electric flux through the surface S is
