B. We can also use ‘that’ (instead of who), but you can’t use which for people.
B1. cannot use that for people when we give extra information.
B2. When we are talking about things, we use that or which (not who) in a relative clause.
B3. That is more usual than which, but sometimes you must use which.
B4. can leave out who/ which/ that when it is the objective.
B5. cannot leave out who or which when we give extra information.
B6. Sometimes who/ that/ which is the objective of the verb.
B7. When who/ that/ which is the object, you can leave it out.
B8. We can use that at the beginning of the clause.
B9. the position of prepositions (in/ to/ for etc.) can be in the middle of the sentence or at the end of the sentence.
B10. We can say: the day/ the year/ the time etc. ‘something happens’ or ‘that something happens’.
B11. We can say: the reason ‘something happens’ or ‘that/ why something happens’.