by the end of意为“到……末为止”,后可跟过去时间与过去完成时连用,也可跟将来时间,而与将来时连用.
By the end of last term we had learned five English songs.
到上学期末我们已学会五首英语歌曲.
The world population will pass six billion by the end of the twentieth century.
到二十世纪末,世界人口将超过六十亿.