比重不同的药物在制备散剂时采用何种方法最佳（）。
A.将轻者加在重者之上
B.多次过筛
C.搅拌
D.等量递加
E.将重者加在轻者之上
参考答案：E
Most old city walls were _____ down at that time because they were worn _____. [ ]
A. pulled; off
B. pushed; out
C. pushed; off
D. pulled; out
怎样调整发动机的气门间隙？
