—Mike, how about your journey to Mount Huang?

—Everything was wonderful except that our car_________ once on the way.

A．broke into

B．broke down

C．turned into

D．turned down

请用信号量解决以下的“晕独木桥”问题：同一方向的行人可连续过桥，当某一方向有人过桥时，另一方向的行人必须等待，当某一方向无人过桥时，另一方向的行人可以过桥。