Right answer:
a. planta
Planta is the conjugation of the verb plantar that matches the third person singular in the simple present. The simple present tense is used to talk about habitual actions or routines. This tense is also used to describe things that happen now or in the near future. So, we can write and translate this sentence as follows:
Todos pensamos que Yolanda planta su jardín (We all think that Yolanda plants her garden)
