Why Does the Observable Universe Have an "Edge

Multiple Choice

Why does the observable universe have an "edge"?

A) Because there are so many galaxies in the universe that every line of sight eventually hits a galaxy,preventing us from seeing any farther
B) Because the density of neutrinos at the "edge" is so large that photons cannot pass through,preventing us from seeing beyond that point
C) Because absorbing matter prevents us from seeing past a certain distance
D) Because we cannot see any farther than the distance that light has traveled over the lifetime of the universe