Which sentence uses correct punctuation?

a. “i’m afraid i don’t know which way to go, said marilyn, “so i’ll have to stop and ask for directions.”

b. “when i get to graduate school,” robyn said, “i plan to study every day.”

c. why does everyone look so tired? asked our science teacher.

The details about the statues, i believe, are that they're carved from blocks of igneous stone, many of them are partially buried under the ground which to preserve and protect them from the harsh environment on easter island, and many of the facial features have washed away. also, the most well-preserved one is at the british museum in london.these are just guesses from what i can see and what i think i read correctly. i'm sorry i couldn't be more .