题目

A元素的最高正价和负价的绝对值之差为6，B元素与A元素的原子次外层上电子数均为8，A与B可形成化合物BA2，则该化合物是A.MgCl2             B.CaF2                 C.SiO2                 D.CS2 答案：A解析：根据题中提供的关于A的化合价信息知，A是卤素，且不是氟(氟无正价)。Some experts predicted that the tourism in China needed three years to recover because of SARS         in Guangdong and Beijing earlier that year. A．occurring          B．occurred          C．to occur          D．being occurred