A new influx of unprecedented private investment should create a bright new future for manned space exploration,
making the possibility of commercial space tourism much more viable than 10 years ago.
(A) making the possibility of commercial space tourism much more viable
than 10 years ago -
wrong comparison. Here we are comparing "the possibility of commercial space tourism" with "10 years ago"(B) and make the possibility of commercial space tourism much more viable
than 10 years ago -
Same as A(C)
making the possibility of commercial space tourism much more viable than it was 10 years ago -
Here the present participle phrase at the end of the clause modifies the entire preceding clause and shows the results of the actions mentioned in the preceding clause.(D)
and make the possibility of commercial space tourism much more viable than it was 10 years
in the past -
"in the past" is wordy(E) making the possibility of commercial space tourism much more viable
than 10 years in the past -
Same as A