Question

— Why are you so popular with your students?
— As a teacher, I seldom give my students so difficult a problem ____ they cannot work out.

A．as

B．that

C．if

D．which

Answer 1

A

考查定语从句。先行词为a problem，后面的从句they cannot work out后缺少宾语，所以使用关系代词，so… as，为固定搭配，所以选A。