Study of $D\to K/\pi e \nu_e$ and measurement of $|V_{cs}|$ and $|V_{cd}|$

Using a 281 pb$^{-1}$ data sample comprised of 1.8 million $D \bar{D}$ mesons collected at the $\psi(3770)$ with the CLEO-c detector, we measure absolute branching fractions as a function of $q^2$, the invariant mass of the $e^+ \nu_e$ pair, for $D^0 \to K^- e^+ \nu_e$, $D^0 \to \pi^- e^+ \nu_e$, $D^+\to K_S^0 e^+ \nu_e$ and $D^+ \to \pi^0 e^+ \nu_e$. We measure the absolute magnitudes of the form factors $f^+_{K}(0)$ and $f^+_{\pi}(0)$. Using unquenched lattice QCD calculations of the form factor normalizations we extract the magnitudes of the CKM matrix elements $V_{cs}$ and $V_{cd}$. Our measurement of $|V_{cs}|$ is the most precise direct determination to date. An extension of the analysis with the $\approx 800~pb^{-1}$ complete data set is also discussed.