ОТНОСИТЕЛЬНЫЕ МЕСТОИМЕНИЯ who и which

Типичные ошибки:

The girl which is speaking to Tom is my sister. => The girl who is speaking to Tom is my sister.

The puppy who is sleeping is very nice. => The puppy which is sleeping is very nice.

Относительные местоимения служат для связи придаточного предложения с главным. Местоимение who употребляется только по отношению к человеку, а местоимение which - только по отношению к предметам и животным.

The man who is standing at the door is our new teacher.

The book which you gave me is very easy.