afe是形容词，名词词性，例如：
1、Employers should provide a safe working environment， as far as is reasonably practicable.只要条件许可，雇主就须提供安全的工作环境。
2、People must be satisfied that the treatment is safe.人们必须确信这种治疗方法是安全的。
3、We were glad she let us know she was safe.她告诉我们她平安无事，我们很高兴。
