巷道断面形状轮廓线属于曲线形的是：（）、（）、（）。
参考答案：半圆拱形；圆弧拱形；三心拱形
The tourists screamed their _____ down to a safe landing when they were sitting in a car that "fell" through
the air from a tall tower. [ ]
A. direction
B. road
C. way
D. voice
简述N、P、K的生理作用。
