— Who did it sound like? Anybody you know?

— Well, perhaps Jeff. I ____ who was calling before he hung it up. [ ]

A. must have asked

B. needn't have asked

C. couldn't have asked

D. should have asked

下列描述的过程中一定有新物质生成的是

A．有热量吸收或有热量放出的变化

B．石墨转换为金刚石

C．有化学键断裂和形成的变化

D．将含钠元素的物质在酒精灯火焰上灼烧