In a Situation Where an Object Can Move Only Along $x$

Short Answer

In a situation where an object can move only along the $x$ axis, a book states "the force on the object is $\mathrm{F}=$ $k x$ , where $k$ is a constant, and $x$ is the object's position coordinate." Is $F$ being used here as a shorthand symbol for $|\vec{F}|(A)$ or $F_{x}(C)$ ?
$\bullet$ A
$\bullet$ C