Your answer should be WHO.
Think of it like this: You wouldn't say "The boy it (a variant of 'which')", because it simply just sounds odd. Instead, you're wired to think "The boy, he (an unknown name, so it would be 'who')".
One afternoon, an old man ordered in a nearby restaurant for breakfast.
He went inside, find a seat and sit comfortably.
Then one smiling waiter approached him and asked: "What's your order for this morning, sir?" The old man replied, "Can I have one rubbery egg and two slices of burnt toast, please?"
The waiter with his two brown eyes glow with awe, answered, "One rubbery egg and two slices of burnt toast? (with an emphasis on the word "rubbery and burnt") Was that correct sir?" "Yes, you just said it right", the man replied.
"Why on earth would you want such a dish?" asked the waiter.
"My wife was out of town and I missed her cooking." replied the old man.
"Oh! I see". the waiter answered with a smirk and walk back scratching his head.
In the sentence "They say we will not be able to afford to own houses in a few years." there's a <u>pronoun reference</u> error. It is unclear who the pronouns<em> they </em>or <em>we </em>are referring to.
Pronouns are used to replace nouns, and it is considered to be a pronoun reference error when the reader is unable to deduce from the text the noun being replaced by the pronoun.
