用that ,which ,where 填空：1、This the factory ____ his father used to work .
2、This is the city ____ I have been expecting to visit .
3、She is looking for her bike ____ she lost yesterday .
4、A new school building will be buuilt _____ there used to be a market.
5、After living in Paris for fifty years ,he returned to the small town ____ he grew up as a child .
6、When you read a book ,you'd better make a mark at the part ____ you don't understand .