There are ______ floors in the building and my home is on the ______ floor.
A:twenty; fifteenth
B:twenty; fifteen
C:twentieth; fifteen
D:twentieth; fifteenth
通过电阻R的电流强度为I时,在t时间内产生的热量为Q,若电阻为2R,电流强度为I/2,则在时间t内产生的热量为()
若点P1,1为圆x2+y2-6x=0的弦MN的中点,则弦MN所在直线方程为( )