What vs. which

[nara]

English Grammar Tests, Elementary Level

ESL/EFL Test #93 "Why Questions", question 2

......... is measured by the Richter Scale?

(a) What
(b) Which
(c) Where
(d) Who

English Grammar Tests, Elementary Level

ESL/EFL Test #93 "Why Questions", answer 2

What is measured by the Richter Scale?

Correct answer: (a) What
_________________________

why what?

[Conchita]

'What' is the correct option here, because the question is about what thing among an unlimited number of possibilities. 'Which' refers to what thing from a small or limited number of answers.

[Daemon99]

1) What book are those lines from?
2) Which book are those lines from?

Can someone please tell me which of the above sentences sounds natural? When do I use what and when which?
_________________
Non-native speaker of English
=================================
I intend to live forever - so far, so good.

[Kitosdad]

Good afternoon Daemon. I believe that the first is the correct form to use.

1) What book are those lines from?

Which would be used when there are only a couple of items to choose between. What is used where a limitless number of items are in question.
_________________
If you need me, I'm here.