Yes. All of them did it. Look at these websites.
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I also do think that Yoona changed the least but she also did do plastic surgery on the corner of her mouth. Before surgery, the corner of her mouth points down while after surgery, the corner of her mouth points up.
For Yoona, it's a little complicated. People tend to think that she didn't do plastic surgery because her after surgery look is similar to her childhood looks. For her, go to this website.
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I am not bashing them or anything but it's because this is a hot topic and it's something that everyone wants to know. I won't hate them just because they did plastic surgery but didn't admit it. Who wouldn't do plastic surgery anyways when they can turn prettier.