Current versus time and voltage versus time graphs of circuit element are shown below. The type of circuit element is

In case of a capacitor,  $q=CV$
 $\therefore i=\frac{dq}{dt}=C\left(\frac{dV}{dt}\right)\mathrm{.........}\left(1\right)$
From the graph given  $\frac{dV}{dt}=\frac{4}{4}=1V{s}^{-1}$
Therefore if  $C=1F$, from equation  $\left(1\right) i=1\times 1=1A\left(\text{constant}\right)$