What is the Nube de Oort and what is believed to come from there?

I- The Nube de Oort is an immense sphere composed of frozen small bodies that encompasses the entire Solar System.
II- Comets that cross the Solar System are believed to come from the Nube de Oort.
a) Only I is correct.
b) Only II is correct.
c) Both I and II are correct.
d) Neither I nor II is correct.