test - Present continuous to discuss action's frequency

I saw the following on an ESL test:

John: How often …………… ?
Dave: He …………… at least five days a week.

a) does he exercise - swims
b) is he exercising - is swimming
c) is he exercising - swims
d) does he exercise - is swimming

I think both (a) and (b) are acceptable and the test isn't standard. Please correct me if I'm mistaken.

Answer

As a native speaker, I would expect ESL test questions to be blatantly obvious to me, such that all the wrong answers are clearly things that only non-native spakers would say. The question here doesn't meet my expectations. Obviously (a) is the most natural without context, but in the right context any of (b), (c), or (d) would be possible for native speakers in some situations.

J.R. gave this conceivable scenario for choice (c) in his comment on the question:

"Have you seen Paul lately?"
"No, why?" "He's looking really good!"
"Really? Lost a lot of weight?"
"Yeah."
"Wow. How often is he exercising?"
"He swims at least five days a week, I think. I'm always seeing him at the pool."
"Good, it's nice to hear about someone keeping their New Year's resolution for a change."

Alcas similarly gave a conceivable scenario for the "is swimming" choices (b) and (d):

"He only used to exercise once in a blue moon, but he's swimming at least five days a week now"

The question is faulty.