The correct answer is A. busqué.
The verb buscar (to look for) in Spanish is a regular verb, which means that you need to learn the rules to create its various forms, and then apply them. In the example above, we need the preterite form of the verb buscar, and it goes like this:
1. yo busqué 1. nosotros buscamos
2. tu buscaste 2. vosotros buscasteis
3. el buscó 3. ellos buscaron
