Top : $\pt$-differential cross section for prompt $\Dzero$, $\Dplus$, and $\Dstar$ mesons in pp collisions at $\sqrts=2.76 $TeV compared with FONLL[7, 27] and GM-VFNS [6, 31] theoretical predictions. Bottom: the ratio of the measured cross section and the central FONLL and GM-VFNS calculations.