China's YouTube just launched globally, and it makes you pass a 100-question exam before you can post a comment. 291 million people have already passed. Bilibili's signature feature is danmaku, comments that fly across the video itself while you watch. That creates a brutal design problem. On YouTube, a troll lives below the fold. On Bilibili, a troll is on screen, over the content, for every single viewer. So they gated it. Answer 100 multiple-choice questions on comment etiquette and…