Given context$-$free grammars that generate the following languages$/$ regular expressions. $(15$ Points$)$

a$)$ r$=($ab$)*$a

b$)$ L $=\{($a$,$ b$)|$ b n a $*$ b n$,$ n $>=0\}$

c$)$ All strings of a and b that include the substring baa

d$)\{$w in $\{0,1\}*|$ w contains at least three $1$s$\}$

e$)$ L $=\{$anbm: n $<=$ m $+3\}$