曼哈顿语法-平行问题

Krystalliming

• 各位大神们，我想问一下为什么答案在修改时，确认了完成时态呢？直接改为了which have been shaken by
  
  
  Tobacco companies, shaken by a string of legal setbacks in the United States, but which retain strong growth prospects in the developing world, face an uncertain future.