Question

This is _______ difficult problem that few students can work it out.

A．so

B．so a

C．such

D．such a

Answer 1

D

so或such……that表示如此……以致的意思，so后跟形容詞或副詞，而such后跟名詞，可數名詞單數需加不定冠詞a或an，本題的problem是可數名詞單數，故填such a，故本題選D。