甲、乙签订一份买卖合同，后由于丙的原因，造成甲未履行合同义务，则向乙承担违约责任的主体是( )
A．甲 B．丙C．甲或丙 D．甲和丙连带
参考答案：A
According to the speaker, what do people often think about astronomers a. They spend most of their time looking through telescopes. b. They are constantly analyzing data. c. They often live near observatories. d. They devote a lot of time to theoretical problems.
平板显示器一般是指显示器的厚度小于显示屏幕对角线长度1/4的显示器件，其中本身不发光的是( )。
A．液晶显示(LCD) B．等离子体显示(PDP) C．场发射显示(FED) D．电致发光显示(ELD)
