HONG KONG—Forty-seven Hong Kong dissidents were charged on Sunday with conspiracy to commit subversion, in the largest single crackdown on the pro-democracy opposition under a Beijing-imposed “national security law.” Sam Cheung, a young activist and a participant in an unofficial primary election last summer, was charged after reporting to a local police station, dressed in a black mask and accompanied by his wife. “Hong Kongers have a really tough time these days,” he told reporters before entering the station. “I hope everyone won’t give up on Hong Kong … (and) fight on.” Cheung was arrested in a dawn raid along with more than 50 other lawmakers and activists on Jan. 6 in the largest so-called national security operation since the law’s passage last June. They were accused of organising and participating in an unofficial primary election last July aimed at selecting the strongest candidates for a legislative council election. The …