托福考试

【单选题】 Among the most complexcrystals are that of silicon dioxide, which has seven different structures at various temperatures and pressures, the most common being quartz.

网考网参考答案：B
网考网解析：
答案：B 分析：改为those，指代crystals.后面的which指代silicon dioxide,所以用单数has 翻译：在最复杂晶体中有二氧化硅的结晶体，二氧化硅在不同温度和压强下有7种不通结构,最常见的是石英。 查看试题解析出处>>