commercial break（广播、电视中插播的）商业广告
A commercial break usually consists of at least two advertising spots; in exceptional cases,however,individual spots are also permissible.There are two kinds of commercial breaks:
Flanking commercial break,placed before or after a program;
Interruptive commercial break,placed within a program.
profit margin [经]利润率；边际利润率
the ratio gross profits divided by net sales