Whenever my grandmother calls just to chat with me I drop everything and enjoy the moment

问题补充：

Whenever my grandmother calls just to chat with me，I drop everything and enjoy the moment，knowing these timespass．

A. call

B. must

C. shall

D. might

答案：

A. call

B. must

(答案→)C. shall

D. might

解析：句意：每当我的祖母打电话和我聊天，因为知道这些时光总会过去，所以我都会放下一切享受这段时光。Shall表示表示一种责任和义务，选C。