Before I set out on my journey my mother told me everything I should pay attention to.A.

问题补充：

Before I set out on my journey, my mother told me everything I should pay attention to.

A. where

B. what

C. how

D. that

答案：

A. where

B. what

C. how

(答案→)D. that

解析：考查定语从句关系词的选择。该句为定语从句，先行词是everything，在定语从句中充当pay attention to 的宾语，

句意为，在我旅行出发前，我的妈妈告诉了我一切我需要注意的东西。