Rules of the Road: INTERNATIONAL ONLY On open water, a power-driven vessel coming up dead astern of...

It isn't wrong. Rule 34(a). You are thinking within a narrow channel in international waters, 34(c).

this answer is wrong. it should be b as I selected for my answer. however, it says the answer is c. in overtaking situation for international the whistle blast start with two prolonged blast followed by either one or two short blast.

As nclevi2 pointed out, "one short blast" is correct. The question specifies you are in open water, as such, sound signals for narrow channels do not apply is this situation. You are simply altering course to starboard.

however, this is also an overtaking situation

Two prolonged before your one or two short blasts is only when overtaking in a narrow channel in international waters when you are overtaking such that the vessel being overtaken also has to move.

Reference Rule 9(e) and 34 (c) (i)

If only the CG took the time to digest the regulations into something meaningful rather than just cut and paste the CFRs into a “handbook.” I, too, was unable to infer initially that overtaking in open ocean was the same as passing.

I thought in open water, no passing signals are required to sound back especially if you don't have to deviate course.
No wiggle, no whistle...

also this question is worded as if my 5 year old wrote it