My 4 year old wants to read the same picture story book again and again, how do I vary it ??

It just like me when i was toddler! Huahahaah Speaking from my point of view, your kid might grow up to be a very good story teller. S/he memorized what you tell and then your kid telling it back to his/her friend. Also, it helps your kid to be attention to details. You don't believe it? Try to eliminate some part of the story. See if S/he notice ot not. I bet they will :)