假设某生态系统中只有甲、乙、丙三种生物，他们的捕食关系如图所示。那么该系统中属于消费者的是

A．甲

B．乙

C．丙

D．乙和丙

President Bush was in Omaha this morning to deliver a speech, but he      the city by the time the shooting took place．

A．left

B．had left

C．had been leaving

D．would have left