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后跟形容词或副词，而such后跟名词，可数名词单数需加不定冠词a或an，本题的problem是可数名词单数，故填such a，故本题选D。