用户请求通过Proxy转发至后端WebServers响应，通过NoSQL服务缓冲后，最终将请求传送到（）

A.五层
B.七层
C.八层
D.六层

A.ansible proxy -m yum -a"name=http：//nginx.org/packages/centos/6/noarch/RPMS/nginx-release-centos-6-0.el6.ngx.noarch.rpm state=present"
B.ansible proxy -m yum-a"name=nginx state=present"
C.ansible app-m yum -a"name=nginx state=present"
D.ansible proxy -m yum -a"name=/usr/local/src/nginx-release-centos-6-0.el6.ngx.noarch.rpm state=present"

A.on
B.yes
C.no
D.out