7. Let $a, b>0$, and
$$
a^{2008}+b^{2008}=a^{2006}+b^{2006} \text {. }
$$

Then the maximum value of $a^{2}+b^{2}$ is ( ).
(A) 1
(B) 2
(C) 2006
(D) 2008
7. B.

Since $a^{2008}+b^{2008} \geqslant a^{2000} b^{2}+b^{2006} a^{2}$, and
$$
\begin{array}{l}
\left(a^{2006}+b^{2006}\right)\left(a^{2}+b^{2}\right) \\
=a^{2008}+b^{2008}+a^{2006} b^{2}+b^{2006} a^{2} \\
\leqslant 2\left(a^{2008}+b^{2008}\right),
\end{array}
$$

and $a^{2008}+b^{2008}=a^{2006}+b^{2000}$,
therefore, $a^{2}+b^{2} \leqslant 2$.