Which one is correct and why?

The method used in this research was terrible.

The method which used in this research was terrible.

The method which is used in this research was terrible.

And about the first one: why 'which' has been left out? To my understanding we cannot omit 'which' where it's a subject of the relative clause.

closed as off-topic by FumbleFingers, Scott, J. Taylor, jimm101, Cascabel Jul 31 '18 at 17:35

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  • Exam questions may be off topic. – Kris Jul 27 '18 at 11:58
  • The method was terrible. Which method? The method (which was) used in the research. The past tense is needed as the research is presumably finished. Leaving out 'which was' shortens the sentence and doesn't make the meaning any less clear. – Kate Bunting Jul 27 '18 at 12:00
  • On the relative clause grammar, it might help to think of 'the method used' as 'the method which one used' which makes method the object rather than subject of the relative clause. – S Conroy Jul 27 '18 at 14:31
  • 1
    You may want to do a search for “whiz-deletion”. There are other questions about this topic on this site: english.stackexchange.com/questions/tagged/… – sumelic Jul 28 '18 at 14:27

As a matter of fact the first example is not a relative clause at all. So nothing had been omitted in the first place.

As 'English grammar in use' says(page 194), it is a '-ed clause'. The word 'Used' is a past participle not past and it has a passive meaning.

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