闭环控制系统的数控车床加工精度高，但结构复杂，维修困难（），常用于加工精度要求很高的场合。
A.成本低
B.保养简单
C.成本高
D.保养困难
参考答案：C
__________about wild plants that they decided to make a trip to Madagascar for further research. [ ]
A. So curious the couple was
B. So curious were the couple
C. How curious the couple were
D. The couple was such curious
伤寒患者，退热1～2周后临床症状再度出现，血培养阳性，应诊断为（）。
A.伤寒复发
B.伤寒再燃
C.并发肠出血
D.并发肠穿孔
E.急性胆囊炎
