2. (2007 Mathematics Olympiad Collaborative Summer Camp Test Paper (I) Question) Given the sequence $\left\{a_{n}\right\}$ satisfies $a_{1}=$ $2000, a_{2}=2007, a_{n+2}=a_{n+1}-a_{n}\left(n \in \mathbf{N}^{*}\right)$, then $a_{2007}$ equals
A. 2007
B. -2007
C. 7
D. -7