几种典型的SDH自愈环中，哪种可以抗多点失效，适合均匀型分布、大业务量应用场合？
参考答案：
四纤双向复用段保护环
—Why didn't you come to Simon's party last night?
— I wanted to, but my mum simply ________ not let me out so late at night. [ ]
A. could
B. might
C. would
D. should
泵的种类很多，归纳起来可分为（）、（）、（）三大类。
