—Doctor, it seems ______ you like to work with animals. —Yes, I think animals should ______ as our friends.

A．that; regard

B．that; be regarded

C．what; regard

D．what; be regarded

有座东西方向架设、可双向通行的单车道简易桥，最大载重负荷为4辆汽车。请定义合适的信号量，正确使用P、V操作，给出任一车辆通过该简易桥的管理算法，解答中请回答下列问题：

给出上述问题的解决算法，结合该算法，简述P、V操作解决该问题的基本思路。