题目

在实验室若不慎把氢氧化钠沾到皮肤上，可以用硼酸溶液处理。下列关于硼酸（H3BO3）的说法正确的是（） A . 硼酸的相对分子质量为62g B . 硼酸中氢元素和氧元素的质量比为1：1 C . 硼酸由氢原子、硼原子、氧原子构成 D . 124g硼酸含有22g硼元素 答案：D—Was his father very strict with him when he was at school？ —Yes, he had never praised him _______ he became one of the top students in his grade. A. after      B. unless C. until      D. when