He is said___________a book on the history of Chinese tone bridge , but I don’t know if he has finished it.

A. to have written   B. to be writing    C . having writing    D writing

根据wlan网络测试规范，进行认证成功率测试时，登录成功上线后，至少（30）s后下线，记为一次认证测试，重复测试（）次。