Gerka finally left the library at midnight, and went home to get a few hours of sleep; he promised himself that he would return early the next morning to finish his research.

What is the correct way to write this sentence?

A Gerka finally left the library at midnight and went home to get a few hours of sleep: he promised himself that

he would return early the next morning to finish his research.

B. Gerka finally left the library at midnight, and went home to get a few hours of sleep; he promised himself that

he would return, early the next morning to finish his research.

C. Gerka finally left the library at midnight, and went home to get a few hours of sleep; he promised himself, that

he would return early the next morning to finish his research.

D. Gerka finally left the library at midnight and went home to get a few hours of sleep; he promised himself that

he would return early the next morning to finish his research