What is the language generated by the following grammar: S $->$ aS $|$ Sb $|\backslash$epsi

A$.$ The set of all strings that with $\text{'}$a$\text{'}$ and end with b$,$ including $\backslash$epsi $.$

B$.$ The set of all strings that contain an equal number of $\text{'}$a$\text{'}$s and $\text{'}$b$\text{'}$s$,$ including $\backslash$epsi $.$

C$.$ The set of all strings that contain an even number of $\text{'}$a$\text{'}$s followed by an even number of $\text{'}$b$\text{'}$s$.$

D$.$ The set of all strings that contain n $\text{'}$a$\text{'}$s followed by m $\text{'}$b$\text{'}$s$,$ where n $=$ m $>=0$

E$.$ None of above.