Are "that", "who" and "which" in these sentences necessary or optional?

• I think blue is the colour that optional __________ I like best.
• Simon, who necessary__________ is 25, got married last week.
• My car has a mechanical problem that /which necessary __________ is expensive to repair.
• He left the keys that optional __________ I gave him on the table.
• The carpenter whonecessary __________ made my book shelf is a rich man.
• He took a plane that necessary __________ left from London.
• The money which optional _______ you borrowed was not really necessary.
• James is the most honest person that optional _______ I have ever met
• They are the people whonecessary _________ live next door.
• The idea, which necessary__________ was very original, has been accepted.
• The book that / which optional________ I bought is very interesting.