I am being confused by this question.

[mylancuocy]

There is a concern among people____if the house prices keep rising,____means it will still be very hard or even life-long project to buy a house.
A.which;which B.that;which C.that;that D.which;which

At first, I believed the answer is B but it is C. However, I cannot understand why answer B cannot be.

[Tdol]

Where did you get this question?

if the house keeps rising

This is wrong- it should be something like if house prices keep rising. I wouldn't use any of the answers without editing the sentence.

[mylancuocy]

This sentence was not written by me. It is from a practice question.
I edited the sentence to be what you thought appropriate.
(original:There is a concern among people____if the house keep rising,____means it will still be very hard or even life-long project to buy a house.)

Now, could you please explain the question?

[Raymott]

This sentence was not written by me. It is from a practice question.
I edited the sentence to be what you thought appropriate.
(original:There is a concern among people____if the house keep rising,____means it will still be very hard or even life-long project to buy a house.)

Now, could you please explain the question?

There's no correct answer. The sentence is badly formed. C is the least wrong answer. 'Which' cannot go in either of the spaces.
"If the prices keep rising, which means ..." doesn't make sense.

By the way, saying "Now, could you please explain the question?" is a bit impolite.

[mylancuocy]

"Now, could you please explain the question?"
I don't know the way what I said is impolite and I also did not want to mean that.
Why is this sentence impolite? What is the better way to say politely?
Thanks!

[Raymott]

"Now, could you please explain the question?"
I don't know the way what I said is impolite and I also did not want to mean that.
Why is this sentence impolite? What is the better way to say politely?
Thanks!

It's hard to explain. All I can say is that that sentence would usually be spoken in an irritated voice. I'm sure you didn't mean it that way. That's why I pointed it out.
"Now, ..." is not a good way to start. You could have just left off that sentence - it's obvious what you wanted. You could've said, "Can you explain why C is the answer?"
But don't worry about it too much. I almost didn't mention it.