对油气压差理解正确的是（）。

A、进密封油压力大于参考气压力

B、参考气压力大于进密封油力

C、参考气压力等于进密封油压力

D、以上都有可能

Passage Four

How did Benjamin Graham view stock investment

A．He believed that both trading stocks and investing stocks are risky.

B．He regarded investing stocks equally risky as trading stocks.

C．He insisted that trading stocks were less valuable than investing stocks.

D．He compared hot stocks to fashionable dogs.