Pop Star Look A Likes

Is it just us, or are today's "pop stars" starting to look the same? Can you name any of these four, because, pictured together like this, we're buggered if we can. And no, that's not Sienna Miller. Three of them are regular visitors to the top 10 singles chart, one has yet to achieve this, though our sources reveal she did once go to the same school as one of the other more popular ones.