deb?http://mirrors.aliyun.com/ubuntu/?precise?main?restricted?universe?multiverse
deb?http://mirrors.aliyun.com/ubuntu/?precise-security?main?restricted?universe?multiverse
deb?http://mirrors.aliyun.com/ubuntu/?precise-updates?main?restricted?universe?multiverse
deb?http://mirrors.aliyun.com/ubuntu/?precise-proposed?main?restricted?universe?multiverse
deb?http://mirrors.aliyun.com/ubuntu/?precise-backports?main?restricted?universe?multiverse
deb-src?http://mirrors.aliyun.com/ubuntu/?precise?main?restricted?universe?multiverse
deb-src?http://mirrors.aliyun.com/ubuntu/?precise-security?main?restricted?universe?multiverse
deb-src?http://mirrors.aliyun.com/ubuntu/?precise-updates?main?restricted?universe?multiverse
deb-src?http://mirrors.aliyun.com/ubuntu/?precise-proposed?main?restricted?universe?multiverse
deb-src?http://mirrors.aliyun.com/ubuntu/?precise-backports?main?restricted?universe?multiverse

從提示信息看出你使用的軟件源信息不完整，國內比較好的推薦http://mirrors.aliyun.com/?阿里云的源每天都與官網主服務器同步一次。