Below is a drawing of all $ 26 $ letters in the English alphabet. As drawn below, some of these letters could be portions of the graph of a function, and some cannot. For example, the $ \textsf{O} $ resembles an ellipse, which cannot be part of the graph of a function. As drawn below, which of these letters could be portions of the graph of a function? (You may not rotate them.) Give your answer as a list of letters with no spaces or other punctuation between them, in alphabetic order. $$\begin{array}{c c c c c} \textsf{A} & \textsf{B} & \textsf{C} & \textsf{D} & \textsf{E}\\\\ \textsf{F} & \textsf{G} & \textsf{H} & \textsf{I} & \textsf{J}\\\\ \textsf{K} & \textsf{L} & \textsf{M} & \textsf{N} & \textsf{O}\\\\ \textsf{P} & \textsf{Q} & \textsf{R} & \textsf{S} & \textsf{T}\\\\ \textsf{U} & \textsf{V} & \textsf{W} & \textsf{X} & \textsf{Y}\\\\ && \textsf{Z} && \end{array}$$