近几年来，“公民上书“现象屡见不鲜。先是孙志刚案件引起3位公民上书全国人大，建议审查《城市流浪乞讨人员收容谴送办法》；接着由周一超杀人案引起1611位公民上书全国人大常委会，要求对公务员录用限制乙肝病毒携带者的规定进行违宪审查；再就是543位公民上书国家有关部委，呼吁抑制药价，解决人民群众的医疗困难问题。
请你运用政治生活有关知识，谈谈对“公民上书”现象的认识。
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