The majority of rural migrants are engaged in the most painstaking, most tiring and dangerous work, _______ college graduates are reluctant to do. A. while B. that C. what D. which 答案:D
下列实验操作中,能达到实验目的的是
[ ]
A.检验氢气纯度时,没有听到任何响声,表明氢气已纯净
B.用适量的水能区分硝酸铵固体和氢氧化钠固体
C.粗盐提纯实验中,蒸发结晶直到滤液蒸干时停止加热
D.用PH试纸测定溶液酸碱度时,先将PH试纸用水润湿,然后再测定