Question $4(10$ points$)$

Given an alphabet $=\{a,b\}$ and a language $L$ consisting of all strings of length $3$ that begin with a$,$ which of the following is the set of all strings in $L?$

$\{$a$,$ aa$,$ ab$,$ aaa, aab, aba, abb$\}$

$\{$a$,$ aa$,$ ab$\}$

$\{$aaa$,$ aab, aba, abb$\}$