41. During her study in Massachusetts Institute of Technology she has got the degree _____ PhD, and it is a degree ______ chemistry.

A．of; at

B．in; at

C．of; in

D．in; of

破底清筛轨枕底道砟连续3根及以上，进行人工捣固作业，施工结束，开通后列车限速的速度阶梯是第一列15km/h，第二列25km/h，第三列45km/h，不少于4h，以后60km/h、80km/h、120km/h各不少于（），其后正常。