Her uncle ___ to New York now, he ___ there twice. He'll be back tomorrow.
用下列词语造句
①造诣
②私塾
The fact that Mary was foreign made ________difficult for her to get a job in that country.
若将铝、铁、氯、硅、氢、氧、锌、硫、磷、铜、氮、碳、银、钙等分成A和B两组,且A组中必须包括氧,应该如何分?试把分组结果用它们的元素符号表示出来:
A组:____;B组:____。