题目

The Pulitzer Prize board announced Wednesday that paper submissions would no longer be accepted and all submissions _____ be done online．        A．could         B．may                 C．can                     D．must 答案：D镁带在耐高温的密闭容器中（内含空气）加热，则下列图中能正确表示容器内所盛物质总质量变化的是 (      )