Unlike the other major planets, Pluto has a highly eccentric orbit, which is thus closer to the Sun than Neptune is for 20 years out of every 230-year cycle, even though it is commonly described as the remotest planet in the solar system.
A) Pluto has a highly eccentric orbit, which is thus closer to the Sun than Neptune is "which" refers to "eccentric orbit". Thus, the orbit is being compared to the Planet Neptune. Eliminate.
B) Pluto has a highly eccentric orbit and is thus closer to the Sun than Neptune is Correct answer - "thus" tells us the eccentric orbit is the reason for Pluto being X, and hence Pluto is then compared to Neptune.
C) Pluto's orbit is highly eccentric and is thus closer to the Sun than Neptune "Pluto's orbit" is being compared to "Neptune". Eliminate.
D) the orbit of Pluto is highly eccentric and thus closer to Sun than Neptune Same comparison error as in (A) and (C). Eliminate.
E) the orbit of Pluto is highly eccentric, thus closer to the Sun than Neptune is Same comparison error as in (A), (C) and (D). Eliminate.