单项选择题
A computer is a machine designed to （）.
A．perform work mathematically B．perform complicated calculations C．store and select information D．all of the above
单项选择题 To be a good salesman, the most important thing is to （）.
单项选择题 Only ______ making investigations ______ have the right to speak.
单项选择题 Thinking that you know ______ in fact you don"t is not a good idea.
