I haven't read any of the books ____ I got for Christmas.
WHICH / THAT / possible to omit
That's the cave in ____ four explorers slept.
WHICH
The dinner for _____ I paid was very expensive.
WHICH
There's the man ____ flew around the world alone.
WHO / THAT
I recently went back to the town _____ I was born.
WHERE
Do you know the girl to _____ John is talking?
WHOM
This is the river in _____ my children love to swim.
WHICH
The girl with _____ he fell in love left him after a few weeks.
WHOM
She worked for a man ____ used to be an athlete.
WHO / THAT
This is the woman ____ climbed the Everest last summer.
WHO / THAT