Great changes __________ in China in the past few years.

A． were taken place

B． took place

C． have been taken place

D． have taken place

在网络上的某台主机，其IP地址为129.56.189.41，它属于 (63) 地址。若已知子网掩码为 255.255.240.0，那么该主机所在的网络号是 (64) 。

A．129.56.189.0

B．129.56.89.0

C．129.56.176.0

D．129.56.189.255