China is a big country. The weather in the south(南方)is different from that in the north(北方). Beijing is a beautiful city of China. In this city, spring is warm; summer is hot; autumn is cool and winter is cold. But in the south of China, it is always warm. In Hong Kong and Sanya, people like to swim in the sea. They can't see snow. In the north of China, people can make snowmen and play with snowballs in winter. People like to spend their holiday(度假) in the south in winter, and in the north in summer.

下列对动物细胞培养的有关叙述正确的是（   ）

中国出现的第一条正式投入运营的铁路是（     ）