What's the subject pronoun in the sentence below. Tell her that her parents will pick her up.

A possessive is missing in the sentence. It is highlighted and corrected below:

A group of young French doctors began the organization Doctors Without Borders in 1971. The founders mission was to help victims of war and natural disasters. → The founders' mission was to ...

Explanation:

One way of expressing possession in English is by using the genitive case, which consists of adding an apostrophe or 's to the possessor in a sentence. For example, if a book belongs to my friend Anna, I can say: Anna's book.

When we have a plural noun that already ends in -s, we should only add an apostrophe to indicate possession. That apostrophe is precisely what is missing in the sentence we are analyzing here. The second part of the sentence is about a mission. Whose mission is it? It is the founders' mission. Thus, we must use the apostrophe for the sentence to be correct.