1、At that time I was a little boy, and I dropped my hatchet unwarily into the river.
那時候我人小，不小心把手上的柴刀掉到河里。

2、That time I was a little boy, and I dropped my hatchet unwarily into the river.
那時候我人小，不小心把手上的柴刀掉到河里。

3、He unwarily tread upon a viper asleep just before his feet
他不小心踩到正睡在他腳前的蛇上。