1. It was not until 1920 _______ regular radio broadcasts began.
A. while B. which
C. that D. when
答：C．在强调句型中，被强调的部分是时间状语或地点状语时，后边不能用when或where，须用that．所谓强调句型就是强调句中的某个成分．如：I saw him at the station yesterday．
可以强调句中的主语、宾语、地点状语或时间状语，被强调部分是人时后边可用who或that．如
It was I who saw him at the station yesterday. 强调主浯
It was him that saw at the station yesterday. 强调宾语
It was at the station that saw him yesterday. 强调地点状语
