A:had played; did
B:played; did
C:had played; was going to do
D:was playing; was going to do
具有“活化石”之称的一组植物是
如图1所示,电源电压不变,滑动变阻器的滑片P从a端滑到b端的过程中( )
定义域为R的函数fx满足fx+2=2fx,当x∈0,2)时,fx=x2-x,x∈0,1)-12x-32,x∈1,2)则当x∈-4,-2)时,函数fx≥t24-t+12恒成立,则实数t的取值范围为( )