3. A student goes upstairs from the first floor to the third floor for class, with a total of 30 steps. However, he moves forward and backward randomly on the stairs. When he stops after moving from the 1st step to the 9th step, he thinks: If all the backward steps were turned into forward steps, he would be
(1) possibly standing on the 30th step
(2) impossible to be standing on the 30th step.
(3) impossible to be standing on the 29th step
(4) possibly standing on the 28th step.
The definitely correct statement is ( ).
(A)(1)
(B)(2)
(C)(3)
(D)(4) $\quad 2-1$
3. B.

Let the total grade improvement of the student be $x$, and the total grade decline be $y$, then $x-y=9$. Therefore, $x+y=9+2y$.
Since $9+2y$ is an odd number, $x+y$ is also an odd number.
Thus, we know that the sum of the student's improvement and decline is an odd number, so we can eliminate (A), (C), (D).