The last option is correct. Fui al mall y compré un vestido azul.
Explanation: It was 8pm. My sister’s birthday was next day and I needed to buy a gift for her, so I went to the mall and I bought a blue dress (fui al mall y compre un vestido azul).
Yes. The president is a person, so you will need to use conocer + a
It can be “nosotros” or “you and him”
<span>La muchacha es baja.</span>