Subjunctive "if A DOES......, B COULD...."

[michaell423]

Hi Ron,

Can you help me better understand the structure below please?

"if A DOES......, B COULD...."

If the new airboat does what it is to be doing -- travel at high speeds undeterred by sandbars, crocodile-infested mudflats, or marshy hippo haunts --it could revolutionize transport on the 2,900-mile-long Congo River.

(A) If the new airboat does what it is to be doing
(B) If the new airboat does what it is supposed to do
(C) If it does as the new airboat is supposed to do
(D) Doing what it is the new airboat is supposed to do
(E) Doing what the new airboat is to be doing

Correct Answer is B.

I assume this is a subjunctive case - its a hypothetical and not ture, however, the Verb in the dependant cluase dont use any past tense verb, how can it make sense?

Thanks, Michael