【May·话题】But conspiracy theorists mutter that the bug could have escaped from one of the city’s laboratories, at least two of which research into infectious diseases.问大佬们一个问题。后面的at least two of which research into infectious diseases. 这句话是从句还是主句啊？有省略的现象吗？能不能帮我分析一下这个从句的结构吗？谢谢各位。