—You didn’t seem to enjoy your meal very much. —It’s not that. I am just . A. on a dietB.

问题补充：

—You didn’t seem to enjoy your meal very much.

—It’s not that. I am just .

A. on a diet

B. on diets

C. go on a diet

D. making a diet

答案：

(答案→)A. on a diet

B. on diets

C. go on a diet

D. making a diet

解析：“你似乎不爱吃肉”“不是，我在节食” be on a diet“节食”系表结构表示状态；go on a diet “节食”强调动作。 根据语境应是强调状态所以选A