$31$ Answer the following questions regarding the contex$-$free grammer $G$ :

$RxRx|S|$

$S$aTb$|bTa|$

$TxTx|x|$

$xa|b|$

I$)$ What are the variables of $E?$

II$)$ what are the terminals of $G?$

III$)$ what is the start var iable of G$?$