The picture shows velocity-time graphs of movements of cars \( A \), \( B \), \( C \) and \( D \). Which of the cars speeds up with constant acceleration of \( 0.8\,\frac{\mathrm{m}}{\mathrm{s}^2} \)?
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Hint: An acceleration \( a \) is the rate of change of velocity \( \Delta v \) of an object with respect to time \( \Delta t \), i.e. \( a=\frac{\Delta v}{\Delta t} \).