って vs が. JLPT question

Question

I'm looking through JLPT N3 questions and have come across this one:

A: ねえ　（　　　）　どんなひと？
B: とても親切でいい人だよ

The possible answers are:

1. 田中さんが
2. 田中さんで
3. 田中さんって
4. 田中さんでも

Number 4 makes no sense at all. "Tanaka-san but"?

Number 2 is a bit weird. We're not doing anything with Tanaka. It is wrong.

However, my instinct was that number 1 was correct. It is not. 3 is. I understand the use of って。 Its saying on the subject of whatever->this. But が also seems that it would work fine. Tanaka is the object we're talking about.

Why is 1 so wrong and 3 has to be right?

Also, would は be strictly okay in this sentence?

Answer 1

「って」 is the only correct answer here.

When someone asks the question 「ねえ, 田中さん（　　　）どんなひと？」, the asker should basically have no knowledge of Tanaka, correct?

That is where the topic-introducing 「って」 comes into place --- "this Tanaka guy", "this guy called --- what was his name, Tanaka?", etc.

Using 「が」 is very unnatural (I would call it plain wrong, actually) when asking about something/someone you know little to nothing about. You say 「これはなんですか。」 and never 「これがなんですか。」.

Regarding 「は」, which is not among the choices given, it is "possible" to use it. BUT it requires a certain condition under which the question 「ねえ、田中さんはどんな人？」 is asked. The condition is that the asker has already asked about at least one other person before asking about Tanaka. If Tanaka is the only (or first) person you are asking about, the only correct choice is to use 「って」.