单项选择题
A．The teachers did lots of writing on the board. B．The teachers were invited to attend several lectures. C．The students were professors from a university. D．The students were studying science and humanities.
A．a bank is closed for one or more days B．too many depositors try to draw out their money at one time C．there is not enough money to pay all its depositors at one time D．tellers of a bank take their own money from the bank