1. Based on the given data set, among which the first 13 data are the training set data, and the rest are the test set data. The data set has four attributes (theory, experiment, homework and grade). 1) Calculate and determine the root node of the decision tree (15 points).

2) Draw the first layer of the decision tree (5 points).

\begin{tabular}{|c|c|c|c|c|} \hline Index & theory & experiment & homework & grade \\ \hline 1 & good & H & A & Excellent \\ \hline 2 & good & M & Not A & Excellent \\ \hline 3 & good & L & A & Good \\ \hline 4 & good & H & Not A & Excellent \\ \hline 5 & ordinary & H & A & Excellent \\ \hline 6 & ordinary & M & A & Good \\ \hline 7 & ordinary & L & A & Good \\ \hline 8 & ordinary & L & Not A & Pass \\ \hline 9 & ordinary & H & A & Good \\ \hline 10 & bad & H & A & Good \\ \hline 11 & bad & L & A & Pass \\ \hline 12 & bad & M & A & Good \\ \hline 13 & bad & L & Not A & Pass \\ \hline 14 & bad & M & Not A & Pass \\ \hline 15 & bad & H & Not A & Good \\ \hline \end{tabular}