Answer:
They
Step-by-step explanation:
she / he are not answers as they are singular nouns, we are dealing with a group of people.
Now read through the sentence with our remaining two options:
The girls had to go back and look at the article again before they could answer the question.
This sounds right, now let’s check the other answer just to make sure.
The girls had to go back and look at the article again before them could answer the question.
This doesn’t sound right, so we’ll answer with “they”