黄河水能资源最丰富的河段是[ ]
A．上游
B．中游
C．下游
D．第三阶梯河段
答案：A
The manager ___ the workers how to improve the program since 9 a.m. [ ]
A. has told
B. is telling
C. has been telling
D. will have told
灶心土的主要作用是
A．增强补脾止泻的功能
B．增强活血化瘀的作用
C．增强止血作用
D．降低毒性
E．减少副作用
