Which of the Following Is a Reason That Astronomers Have

Which of the following is a reason that astronomers have not found giant planets with the orbit of Neptune around other stars?

A) our theories suggest that orbits as far away from a star as Neptune are never stable (and the presence of Neptune in our own solar system is a big mystery)
B) Neptune takes 165 years to go around the Sun; getting information about just one cycle of such a planet's orbit around another star would take astronomers 165 years
C) at the orbit of Neptune, only very low-mass planets (smaller than Mercury) can form
D) the method we are using to find planets currently can only reveal low-mass planets, while we expect high-mass planets at the orbit of Neptune
E) you can't fool me; we have already found several planets as far from their stars as Neptune is from the Sun