Alejandro estudia para el examen.
The correct answer is the second one.
Spanish verbs have suffixes for each of the pronouns, just like English does (only for the third person singular). So, this is how you conjugate the verb estudiar in Spanish:
1. yo estudio 1. nosotros estudiamos
2. tu estudias 2. vosotros estudiáis
3. el/ella/Usted estudia 3. Ellos/ellas/Ustedes estudian
