Unlock the following officers by completing the corresponding challenge scenarios:

OFFICER - CHALLENGE SCENARIO
Cui Zhouping - Hunting Dong Zhuo Challenge Scenario
Guan Ning - Guan Du Skirmish Challenge Scenario
Lu Baishe - Mai Castle Escape Challenge Scenario
Meng Jian - Liu Bei's Subjugation Challenge Scenario
Shi Tao - The Turbans' End Challenge Scenario
Wang Tao - Nanman Rebellion Challenge Scenario
Wang Yue - Defense of Jie Ting Challenge Scenario
Zhang Shiping - Huang Zu Challenge Scenario