a) These are the boys with whom I went on holiday.These are the boys I went on holiday with.
b) This is the letter for which I've been waiting. This is the letter I've been waiting for.
c) That is the shop from which Sue bought her bike. That is the shop Sue bought her bike from.
d) That is the hotel at which I stayed. That is the hotel I stayed at.
e) Tim is someone to whom I hardly ever write. Tim is someone I hardly ever write to.
f) Do you know by whom this book was written? Do you know who wrote this book by?
g) Ravenna was the most interesting town in which we stayed. Ravenna was the most interesting town we stayed in.
h) United were the best team against which we played. United were the best team we played against.
Ответ: See above.