若函數(shù)f(x)＝a^x+n的圖象經(jīng)過(1，7)點，又其反函數(shù)f^-1(x)的圖象經(jīng)過(4，0)點，則f(x)的解析式是

1. A.
   4^x+3
2. B.
   2^x+5
3. C.
   5^x+2
4. D.
   3^x+4

若函數(shù)f(x)=a^x＋k的圖象經(jīng)過(1，7)點，又其反函數(shù)f^-1(x)的圖象經(jīng)過點(4，0)，則函數(shù)f(x)的表達式為________．