Which of the following is (are) correct about the regular expression a a* b b* c c* d d*?
1. The language for the given expression is L = {aⁿbⁿc^md^m | n ≥ 1, m ≥ 1} ∪ {aⁿb^mc^mdⁿ | n ≥ 1, m ≥ 1}
2. The context-free grammar for the given expression is:
S → AB | C
A → aAb | ab
B → cBd | cd
C → aCd | aDd
D → bDc | bc
3. The language generated by this expression is an equal number of a's, followed by an equal number of b's, followed by an equal number of c's, followed by an equal number of d's.
Choose the correct answer from the options given below:

1. AOnly 1 is correct
2. BOnly 2 is correct
3. CBoth 1 and 2 are correct
4. DAll the three 1, 2 and 3 are correct

Pick an option to check yourself, or open the answer below.