I saw it here.

The Olympic Games have grown from a one-day affair to _____ sixteen days each time it is held.

A. that which lasts

B. one which lasts

In my opinion, both are correct, but I can't tell why...

one and that (and it) always confuse me, can anyone make it clear when to use which? Thanks.

  • 2
    I think it should be one because it engaged a new thing which hasn't been mentioned in the previous context.
    – dan
    Jun 29, 2018 at 9:01

1 Answer 1


The correct answer to your first question is (b), one which lasts... because you haven't introduced or mentioned the thing which you are talking about before.

One (to be used usually when a new thing is introduced):

One thing that I hate the most is when the bus is fully occupied, causing me to wait for another ten minutes.

That (when the audience knows what you are talking about, for example when you both see something)

(pointing at a car) That's the new model I was talking about earlier on!

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