1.I will treasure the time that/which we spent together.
2.As is known to all of us,he is...
3.His father bought a new toy for him,which made...
4.This is the house that/which he lived in as a boy.或 This is the house where he lived as a boy.
5.I still remember the day when I went to the zoo with my parents for the first time.
或者 I still remember the day on which I went to the zoo with my parents for the first time.