relative clauses

prosze o sprawdzenie
1.make one sentence from each group of sentences.
a)I lent you a book. It was written by a friend of mine. She lives in France
The book I lent you was written by a friend of mine who lives in France

b) A woman's jewels were stolen. A police officer was staying in the same hotel. The woman was interviewed by him.
The woman whose jewels were stolen was interviewed by a police officer who was staying in the same hotel

ok

the medicine which the doctor gave me had no effect at all.
dlaczego tu nie może byc which, ani żadnego innego relative pronoun?

nie jestem pewny, ale po rzeczownikach niepoliczalnych nie daje sie relative pronoun?

moze byc albo which albo that, alb tak jak jest - zero relatve pronoun (bez zaimka wzglednego)

ale dlaczego???
jelsli jest to object to możemy pominąć ten zaimek? tak?
bo juz sam nie wiem

jesli jest to object - tak

a w tym zdaniu dlaczego wolno pominac?

no bo zaimek w tym zdaniu jest object of the verb give

dzieki:)

a w ty zdaniu
the shoes I finally bought were the ones I tired on first
tu tez mozna, ale nie trzeba napisac which lub that? tak?

no tak - shoes object of the verb buy

ogolna zasada: jezeli that/which/who oddziela dwa rzeczowniki/zaimki, np. medicine/doctor, shoes/I, to mozna pominac which/that/who
Jak pomyslisz, to dojdziesz do wniosku, ze tam moze byc wylacznie wtedy, jezeli which/that zastepuje object.
Oczywiscie, pamietaj tez o non-defining relative clauses (tych z przecinkiem) - w nich nie mozna usuwac that/which/who

tę zasadę znałem :)
dzięki ENGEE30 i MG za odpowiedź.