Iran that has the world’s fourth-largest oil reserves also has the world’s second-largest natural gas reserves.
(A) Iran
that has the world’s fourth-largest oil reserves also has the world’s second-largest natural gas reserves. - We do not need the essential modifier to modify "Iran" as there is only one Iran.
(B) Iran has the world’s fourth-largest oil reserves as well as
having the second-largest natural gas reserves.
(C)
Iran has the world’s fourth-largest oil reserves and second-largest natural gas reserves.(D)
Iran has the world’s fourth-largest oil reserves; the world’s second-largest natural gas reserves are also in Iran. - Unnecessarily wordy.
(E)
Iran, having the world’s fourth-largest oil reserves, is in addition having its second-largest natural gas reserves as well. - There are multiple errors in this one. "in addition" and "as well" is redundant. It also has meaning error. It basically saying Iran's having the world’s fourth-largest oil reserves is the reason that Iran is having its second-largest natural gas reserves, which does not make any sense.