产品商标的名称研究主要有（）（）（）和易记性。
参考答案：含义；适用性；发音
联合国《制止向恐怖主义提供资助的国际公约》何时生效？我国何时签署？
So far nothing ________ Tom.I want to know the reason ________ he hasn't written to me. [ ]
A．heard from；why
B．has been heard from；why
C．was heard from；that
D．has heard from；that
