Hutong is a kind of ancient typical city 5lrccl in Beijing.____ (surround) the Forbidden City, many were built during the Yuan, Ming and Qing ____ (dynasty). In order to establish the strongest power for emperors, the royal family planned the city and arranged the residential areas (住宅区). The Forbidden City- ____ center of the Beijing city, was the royal palace.

    At the end of the Qing dynasty, after ____ (close) China came under the influence from abroad, many old hutongs lost____ (they) former neat (灵巧的) arrangement.

    After the founding of the People's Republic of China in 1949, the conditions of hutong ____ (improve). But in recent years, the houses in many hutongs have been pulled ____ and then replaced by modem buildings. And the hutong today is fading into the shade for both tourists____ local people.

    However, in the urban district of Beijing, hutongs still occupy one ____ (three) of the total area, providing housing for half population, so many hutongs ____ (survive) these years. In this respect, we see Beijing as an ancient yet modem city.

电话之间互相通话时，一般都是通过____ 来转接的，这样可以提高线路的利用率，电话通信存在____ 信号和____ 信号两种．

将细胞的结构与它的功能连线。