Good question. and @sudsho a genuine doubt.
But as we are using LRU(replace the page that has not been refrenced for a long time), i think decision will be taken on the basis of refrence and modified bit.
Here page $2$ and $3$ are modified, so they will not be replaced. now, $r = 1$ in page $1$ means it is refrenced in last clock cycle while page-$0$ is not refrenced in last clock cycle. So, Page-$0$ will be replaced.