单项选择题
A.属于要约邀请，随时可以撤销
B.属于要约，在水泥运抵施工现场前可以撤回
C.属于要约，在水泥运抵施工现场前可以撤销
D.属于要约，而且不可撤销
单项选择题 W: Would you mind my visiting your class tomorrow morning, Professor Smith?M: No, not at all. But I don’t have classes tomorrow morning. Perhaps you can go to my class on Friday morning.Q: What do we learn from the conversation?（）
单项选择题 A．弥漫性甲状腺肿大伴有血管杂音 B．弥漫性甲状腺肿大伴有触痛C．甲状腺肿大、质硬，表面不光滑 D．放射性核素扫描为冷结节Graves病的典型体征
单项选择题 W: Hurry up, darling. We have to meet your aunt at the railway sta6on at 9:25.M: Don’t worry. We still have 40 minutes to go.Q: What time is it now?（）