Dear Mr. A:

You wrote:
>
> I read this sentsnce in the educational ministry book in Egypt and I
> feel it has a mistake; am i right?
> The sentence:
> Which deveolpment made tourism the massive industry it is today?

This is a question and it makes good sense in English. Another way of asking the same question would be “What development made tourism the massive industry it is today?” However, the word “Which” implies that there are more
than one development, but the question is looking for the best answer.

In this sentence “Which” is an interrogative pronoun, not a relative pronoun.