演说的

It is a hotbed of research.

它是一个研究的热门。

Thus the chemical composition of intermediate A is that of nickel nitrate tetrahydrate, that of intermediate B is of nickel nitrate dihydrate, that of intermediate C is of the monohydrate whilst that of D is anhydrous nickel nitrate.

因此，中间产物A的化学成分是四水硝酸镍，中间产物B的化学成分是二水硝酸镍，中间产物C的化学成分是一水化物，而中间产物D的化学成分是无水硝酸镍。