13. Five friends go to the cinema to watch a movie, and their seats are adjacent from 1 to 5 in a row from left to right. During the movie, Ada goes to the lobby to buy some popcorn. When she returns, she finds that Bea has moved two seats to the right, Ceci has moved one seat to the left, Dee and Edi have swapped seats, and only the leftmost seat is left for her. Then Ada initially sat in seat ( ).
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5
13. B.

Let $(A, B, C, D, E)$ be the initial seat numbers of five people. Then
$$
A+B+C+D+E=1+2+3+4+5 .
$$

Assuming the positive direction is to the right, Ada needs to move $x$ seats, then
$$
\begin{array}{l}
A+x+B+2+C-1+E+D \\
=1+2+3+4+5 \\
\Rightarrow x=-1 .
\end{array}
$$

Thus, after moving 1 seat to the left, Ada sits in seat 1. Therefore, Ada was initially in seat 2.