在图所示的电路中，小灯泡正常发光时电压为6V，电源电压为12V，当图中滑动变阻器滑片向左移动时，灯泡亮度增加，之后突然熄灭，则此时电流表、电压表的示数为（　　）

A．原来正常发光时的两倍

B．电流表示数为零，电压表示数为6V

C．电流表示数为零，电压表示数为12V

D．电流表示数增大，电压表示数为零

During the Renaissance, graphs and diagrams ______.

A．were often used to aid scientific researches

B．served as sources of fresh ideas for some scientists

C．could provide scientists with an immense quantity of knowledge

D．were necessary for the expression of creative ideas