—I’m going to spend my summer holidays in Hawaii.—How lucky! And don’t forget to send me a

问题补充：

—I’m going to spend my summer holidays in Hawaii.

—How lucky! And don’t forget to send me a postcard.

A. That sounds good. B. Have a nice trip! C. Good luck.

答案：

解析：情景交际。That sounds good. 那听起来不错；Have a nice trip! 祝你旅途愉快； Good luck.祝你好运。根据上文，我要去夏威夷度我的暑假。——太幸运了，联系下文，不要忘了给我送一张明信片。结合语境可知选B。

故选B