Sentence Correction

Hi All,

In the below question, the OA is [spoiler]"A"[/spoiler]. Can somebody please tell why [spoiler]"A"[/spoiler] is preferred over [spoiler]"D"[/spoiler] ?

It may be another fifteen years before spacecraft from Earth again venture to Mars, a planet now known to be cold, dry, and probably lifeless.

(A) again venture to Mars, a planet now known to be
(B) venture to Mars again, a planet now known for being
(C) will venture to Mars again, a planet now known as being
(D) venture again to Mars, a planet that is known now to be
(E) will again venture to Mars, a planet known now as being

Thanks
Mohit