People like to live a life full of ________ and there are _______ of life styles available for people to choose in the modern world. A. a variety; a variety B. varieties; varieties C. a variety; varieties D. variety; varieties 答案:D某元素构成的双原子单质分子有3种,其相对分子质量分别为158、160、162,在天然单质中,此三种单质的物质的量之比为1:1:1,由此推断的以下结论中,正确的是( )A.此元素有三种核素B.其中质量数为79的核素占原子总数的1/3C.其中一种核素的质量数为80D.此元素的单质的平均相对分子质量为160