 Complete the following phrase:  Pei Songzhi, who annotated Jia Xus biography in the Sanguozhi, argued that Jia Xus advice to Cao Cao was inappropriate. He pointed out that Cao Caos territories lacked the stability necessary for Cao Cao to do as Jia Xu advised  focus on economic development in Jing Province. Moreover, Cao Cao had to deal with the external threats posed by warlords such as Han Sui and Ma Chao in the northwest. Pei Songzhi noted that Jing Province was highly unstable and would not remain under Cao Caos control for long, because of the polarising effects of the presences of Liu Bei and Sun Quan in the region. He pointed out that during the 