焦油加工的主要任务是获得酚、萘、蒽等纯产品和（）等粗产品。
参考答案：洗油沥青
He is a strict but kind-hearted teacher , _______ his students respect but are afraid of .
A．one whom
B．for whom
C．which
D．that
X线管发出的射线束形状为
A．平行线束
B．锥形线束
C．交叉线束
D．垂直线束
E．不规则线束
