which of the following sentences is correct

which (one) of the following sentences is correct?
of course the last one, i.e. it's they who need to pass the exam.

p.s. the verb of your question is a singular verb, IS, then you should ask which ONE instead of just ask which of the .....................is correct.

It’s him who always does the work.
It’s us who’ll have to pay increased taxes.
these are both correct.
the last one should be 'them ' instead of 'they '

It’s him who always does the work.

"It’s him who always does the work.". this sentence is correct.