A.超声和次声的传播不需要介质
B.光在空气中的传播速度约为340m/s
C.红、绿、蓝被称为光的“三基色”
D.只有声污染,没有光污染
答案:C
At that time, he spent as much time as he can_____the ancient statues which would be sunk in the river.
A.paint
B.to paint
C.painting
D.painted
禁用宫颈旁阻滞法分娩镇痛的有哪些()
A.肝、肾功能不全
B.胎儿宫内窘迫
C.妊高征
D.过期妊娠
E.糖尿病