____makes some people appear astonishingly youthful while others seem much older than their actual age? A.What it is B.What is it that C.What it is that D.Why it is what 答案:B 解析: 考查强调结构的特殊疑问句。句意为:究竟为什么有些人会看起来年轻得让人吃惊,而另一些人却看起来比实际年龄苍老得多?题干缺少主语,因此如果句首只填一个词时应填what,变为强调结构的特殊疑问句则是What is it that...。目前含有元素硒的保健品已开始涌入市场,已知它与氧同主族,而与钙同周期,下列关于硒的有关描述中不正确的是A.原子序数为24B.最高价氧化物为SeO3,为酸性氧化物C.原子半径比钙小D.气态氢化物分子式为H2Se,受热较容易分解