Which of the following graph represent one-one function?

$\text{A function is one–one if }f(x_1)=f(x_2)\Rightarrow x_1=x_2.$

$\text{Graphically, a function is one–one if every horizontal line cuts the graph at most once.}$

$\text{The given graph is a straight line with positive slope.}$

$\text{Thus the function is strictly increasing.}$

$\text{Hence different values of }x\text{ give different values of }y.$

$\text{Any horizontal line intersects the graph only once.}$

$\text{Therefore the function represented by the graph is one–one.}$