Mobikes are very convenient They may sometimes bring trouble to

Mobikes are very convenient They may sometimes bring trouble to road safety. They are not properly used or parked, （compound-complex sentence）
【正确答案】：Mobikes are very convenient, but they may sometimes bring trouble to road safety if/ when they are not properly used or parked.
【题目解析】：根据以上三个单句的关系，我们把第一句为主句，由于第二句的主语与第一句相同，但意思却是转折，所以把第二句处理为but引导的并列句，把第三句处理为状语从句，表示“当使用不当或者停车不当的时候，摩拜单车会给道路安全带来隐患。”