When asked to explain _____ he does to make his students so fascinated with his lessons, the teacher

paused and thought deeply. [ ]

A. what it is that

B. that what it is

C. what is it that

D. that what is that

图是甲、乙、丙三种固体物质的溶解度曲线，根据图示回答：

（1）将t₃℃时，甲、乙、丙三种物质的饱溶液降温到t₂℃时，没有晶体析出的是______．

（2）t₂℃时，甲、乙、丙三种物质溶解度由大到小的顺序为______．

（3）t₁℃时，若将50g的甲物质放入100g水中，充分溶解后，所得甲物质溶液的质量为______．

（4）若将t₁℃时丙的饱和溶液升温到t₃℃时，溶质质量分数会______（填“变大”或“不变”或“变小”）．