如图所示,已知∠AOB=40°,OM平分∠AOB,MA⊥OA于A,MB⊥OB于B,则∠MAB的度数为
A. 50°
B. 40°
C. 30°
D. 20°
答案:D
Folk music can usually ______ senior citizens because of their experiences.
A.express
B.cover
C.play
D.reach
慢性支气管炎咳痰量以()
A.咳嗽后较多
B.清晨较多
C.夜间较多
D.午后较多
E.上述都不是