creating a question given a response

Question

I encountered the following on a test. Write the suitable question for the given response.

R) たけしさんのかばんはそのかばんです。

I wrote the following question to elect such a response:

このかばんはだれのかばんですか。

apparently this is completely incorrect, but I dont understand why.

the correct answer is:

たけしさんおかばんはどのかばんですか。

which is fine and makes sense I just dont understand why what I said makes no sense when I translate it and the response to English it makes sense to me. not sure if im mistranslating it our if in Japanese what i am saying somehow doesn't make sense in Japanese just in English.

Answer 1

The response (as you marked R) たけしさんのかばんはそのかばんです means "Takeshi's bag is that one/bag".

You asked このかばんはだれのかばんですか, meaning "Whose bag is this?". This would be responded to with たけしさんの（かばん）です; "It is takeshi's (bag)".

But the correct answer given points to a specific bag (out of possibly several that are present). So the question needs to say, "Which bag is Takeshi's (bag)?", or "Takeshi's bag is which (one / of the following)?". And for that, the question needs to be as shown in the correct answer; たけしさんのかばんはどのかばんですか。 (It could also use どれですか).

Also, as @FelipeOliveira mentions in the comments, the topic of the response is Takeshi's bag. Thus, the topic of the question should also be Takeshi's bag. In your solution, the topic changes to "this bag", which is why it's not correct.

Summary:

Response:
たけしさんのかばんはそのかばんです　➝　Takeshi's bag is that one/bag.

Question:
○　たけしさんのかばんはどのかばんですか　➝　Takeshi's bag is which one/bag? (Same topic)
×　このかばんはだれのかばんですか　➝　Whose bag is this? (Different topic)

For your given solution:
このかばんはだれのかばんですか　➝　Whose bag is this? ("This bag is whose bag?")

Response:
○　(このかばんは)たけしさんの(かばん)です　➝　(This bag is) Takeshi's (bag); (Same topic, even though it's omitted)
×　たけしさんのかばんはそのかばんです　➝　Takeshi's bag is that one/bag. (Different topic)

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＊注　ー　R is the given "response". correct answer is the solution to the problem of the test; which happens to be a question sentence. Too many overlapping terms! .·´¯'(>▂<)'¯`·.