A:either
B:though
C:but
D:too
已知函数y=f(x)的定义域为R,当x<0时,f(x)>1,且对任意的实数x,y∈R,等式f(x)f(y)=f(x+y)成立.若数列{an}满足a1=f(0),且f(an+1)=1f(-2-an),n∈N+ ,则a2012的值为( )