at the beginning of the 21st century是什麽意思

例句：

China is the world's most populous country, with some 1.3 billioninhabitants at the beginning of the 21st century.

中國是世界上人口最多的國家，21世紀初的人口約有13億。

at the beginning of

[英][?t ? bi?ɡini v][美][?t ?i b?ɡ?n v]

在…之初;

21st Century

n.21世紀;