Which of the following sentences could take the place of: el médico le da una inyección al muchacho.
se la da.
le la da.
la le da.

The sentence could take the place of "El médico le da una inyección al muchacho" is:

- Se la da.

Explanation:

Pitifully, the words from the Spanish: me, te, nos, se don't have direct translation to English, because these words mention the noun directly, then you must learn them and her use which is for the nouns I, you, we, they respectively, the nearest form could be the object pronouns. In the case of "la" that's because the article that works with the noun "injection" in Spanish is that, and the verb maintains its form inside the sentence.