Answer:
Use tú for informal situations such as with a friend, children, young people, people you know very well. Use usted (Ud.) for formal situations such as in a job interview, in a bank, with elderly people, with someone you don't know or you have just met
Explanation:
First Line "EL" Second Line "Yo" & Third Line "Tu"
The answer is C. The question translates to "How many books are there?"
