2. Necessary but not sufficient conditions, there must be such a relationship in geometric series, but not necessarily geometric series, such as 1, 2, 2, 4.

3. The image of function y=f(x+2) is symmetrical about y axis, that is, f(x+2)=f(-x+2), which can be transformed into

f(x)=f(4-x)

So f(4)=f(0)

f(6.5)= f(2.5)= f(4-2.5)= f( 1.5)

f(7)=f(3)=f( 1)

So choose C.