Right answer:
b. doy
Doy is the conjugation of the verb dar for the first 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 here this sentence describes what is happening now, that is, I give ice cream to my cousin today. Therefore:
Sí, yo doy helado a mi primo hoy.