13. The board of directors of Xinhua High-Tech Co., Ltd. has decided to invest 1.3 billion yuan in development projects this year. There are 6 projects to choose from (each project is either fully invested in or not invested in at all), with the required investment amounts and expected annual returns for each project as follows:
\begin{tabular}{|c|c|c|c|c|c|c|}
\hline Project & $A$ & $B$ & $C$ & $D$ & $E$ & $F$ \\
\hline Investment (billion yuan) & 5 & 2 & 6 & 4 & 6 & 8 \\
\hline Return (billion yuan) & 0.55 & 0.4 & 0.6 & 0.4 & 0.9 & 1 \\
\hline
\end{tabular}

If it is required that the total returns from all selected projects must not be less than 1.6 billion yuan, then, when the selected projects are $\qquad$, the total returns from the investments are maximized.
13. $A, B, E$