What is the estimated number of galaxies in the Universe?

I- There are more than 250 billion galaxies in the Universe.
II- The average number of stars in a galaxy is around 150 billion.
III- There are more than 50 billion planets in the Milky Way.
IV- It is estimated that around 500 million planets could harbor life forms.
a) Only I and II are correct.
b) Only II and III are correct.
c) Only III and IV are correct.
d) I, II, III, and IV are correct.