按照原油含油量不同,可以把原油分为三类,即低流原油,含硫原油和()原油.
参考答案:含硫,高硫原油
The reason _____ he explained is ___ she was ill.
A.that , that
B.which , that
C.why,because
D.why, that
个案社会工作有哪些主要特征?