Which is correct ?

[adarsh01]

Which of the following is correct ?


i)The second engine would be used if the first engine failed
(or)

ii)The second engine would be used if the first engine fails.




i)The second engine will be used if the first engine failed.
(or)
ii)The second engine will be used if the first engine fails.


Some one please give some explanation.

I appreciate your help.



Thanks,
Adarsh

[SlickVic9000]

(Not a Teacher)

For the first set, (i) is correct.

For the second, (ii) is correct.

The other choices use the wrong verb tense.