The contrast indicated by 'yet' is the families not being able to afford a hope yet having to shell out more than 25% of their income due to rising rental rates... thats why (C)
Also, I am not sure the grammatical construction of (B) is right..
furthermore usually adds credence to an original idea or presents a new parallel idea and is usually logically independent.. so to have it immediately after a comma seems out of place..
EX: The acceleration performance of this car model is very poor; furthermore, its fuel consumption is extremely high.
In addition (Not using furthermore to avoid confusion!!) there should ideally be a comma after furthermore which is not present here.. hence (B) is not the answer
just my 2 cents though :-o
Can we have the corrent answer as well please!!
Right, I agree on that, however
"The acceleration performance of this car model is very poor yet its fuel consumption is extremely high. also seems far out.
And if you see the sentence, it has two related ideas. They can't buy a house, and they rising rates leave them with less equity.
Where is the contrast here? These seem to be related, as house prices are going up and so are rental rates so they gotta pay more.
) there should ideally be a comma after furthermore which is not present here.. hence (B) is not the answer

This will not fit with the last part of sentence "such firms tend to be very large" as it talks about firms and not the expenditures!!