Which of these is the grammar for a languate AnBn, a string that has n consecutive A$\text{'}$s followed by n consecutive B$\text{'}$s$?$

$=$ empty string $|$ A B $|$ AABB $|$ AAABBB $|...$

$=$ A B

$=$ empty string $|$ A B

$=$ empty string $|$ A B $|$ AA BB $|...$