approximately has400 pages when this book is completed.
当这本书完成时大约有四百页。
A unit of time corresponding approximately to one cycle of the moon's phases, or about30 days or4 weeks.
月大约和月亮盈亏的一个周期相当的时间单位, 或约三十天或四周
At a time near to; at approximately
将近。。。的时候; 大约在。。。