— ________can you travel around the world on the Internet?
—In a day.
A:How often
B:How long
C:How soon
D:How much
下列变化属于生长现象的是( )
已知函数fx=x2+2x,x≥0x2-2x,x<0.若f-a+fa≤2f1,则a的取值范围是( )