On a standard six-faced dice, the letters $a,b,c$ and $d$ are written on the four adjacent side faces in a consecutive clockwise direction, while the letters $e$ and $f$ are positioned on the top and bottom faces respectively. If face $c$ is turned to become the top face, which letter will appear on the bottom face?

Let us trace the spatial layout of the faces on the dice:
* The side faces arranged consecutively in a clockwise circle are $a\to b\to c\to d\to a$.
* In a four-face loop configuration, any face is always directly opposite to the face that is two positions away from it.
* Therefore, face $a$ is opposite to face $c$, and face $b$ is opposite to face $d$.

When face $c$ is positioned on top, the face directly opposite to it will face the bottom. Since $a$ is opposite to $c$, face $a$ will be at the bottom.