It’s been a year since China introduced the controversial national security law in Hong Kong. More than 100 people - including teenagers - have been arrested since then. But what is the law? BBC Hong Kong reporter Danny Vincent explains. The law makes it easier to punish protesters and reduces the city's autonomy. It was introduced after massive pro-democracy protests rocked the city in 2019. China has said the law will return stability. But critics say it restricts protest and freedom of speech. They say that it violates the "one country, two systems" principle under which the former British colony of Hong Kong was handed back to China. This and a mini-constitution are supposed to protect freedom of assembly and speech, an independent judiciary and some democratic rights for Hong Kong - freedoms that no other part of mainland China has. Subscribe to #BBCMyWorld here: https://bit.ly/3wxzdPx