18. A) To protect her from getting scratches.

　　B) To help relieve her of the pain.

　　C) To prevent mosquito bites.

　　D) To avoid getting sunburnt.

　　W: These mosquito bites are killing me. I cant help scratching.

　　M: Next time you go camping, take some precaution, say wearing long sleeves.

　　Q: Why does the man suggest the woman wear long sleeves?

　　C)。四個選項都是不定式作目的狀語，聽音時要注意說話人做事的目的。對話中女士埋怨蚊子咬得她忍不住直撓，男士建議她下次野營時要采取防護措施――穿長袖衣服。可見男士建議女士穿長袖衣服是為了預防蚊子叮咬。故本題答案為C)。