2. Ans: (D)
Other than (D), all numbers are less than $2010^{2010}$. Now $3^{7}>2010$. Thus $2010^{2010}<\left(3^{7}\right)^{3^{7}}<$ $3^{\left(3^{9}\right)}$, the result follows.
2. Among the five integers below, which one is the largest?
(A) $2009^{2010}$;
(B) $20092010^{2}$;
(C) $2010^{2009}$;
(D) $3^{\left(3^{a^{3}}\right)}$;
(E) $2^{10}+4^{10}+\cdots+2010^{10}$.