Let L$=\{$an bn $|$ cn dn $\},$ such that n$>=0\},$

a$-$ give three strings belonging to L$.$ What is the category of this

language? $(3$ marks$)$

b$-$ Find a grammar$-$recognizing language L$.(3$ marks$)$

c$-$ What is the explicit expression of language L$2?(5$ marks$)$

Find a grammar$-$recognizing language L$2.$

d$-$ Select the simplest category of automata that should be used to

recognize a string belonging to L$2.$ Explain how it works while trying

to recognize the following string: cdaabb. $(4$ marks$)$