The film has been on for half an hour.（改为同义句）It----half an hour ------the film--------。
问题描述：
The film has been on for half an hour.（改为同义句）
It----half an hour ------the film--------。
答
It has been half an hour since the film started.
答
It has been half an hour until the film on.
答
The film began half an hour ago.
或
The film has been on since half an hour ago.
或
It is half an hour since the film began.