结束用end还是ending

用end，例如：

1.By the end of the day we were tired but happy.一天结束时，我们很累，但很高兴。

2.I always leave a clear desk at the end of the day.每天工作结束时，我总是把桌上收拾干净不放任何东西。

3.The new model will be in production by the end of the year.新型号将于年底投产。