直流电动机如何分类
参考答案：按励磁方式来分，可分为他励、串励、并励和复励四种。
This book tells ______ life story of John Smith, who left ______ school and worked for a newspaper
at the age of 16. [ ]
A. the; /
B. a; the
C. the; the
D. a; /
原发性免疫缺陷病的治疗原则是什么?
