正确形式：The teacher told us that this was an_(avoid) mistake.

正确形式：The teacher told us that this was an_(avoid) mistake.
正确形式：The teacher told us that this was an_(avoid) mistake.

正确形式：The teacher told us that this was an_(avoid) mistake.
The teacher told us that this was an_avoidable (avoid) mistake.
avoidable ,可避免的.
老师告诉我们这是个可避免的错误.

avoidable
可避免的

avoidable
用形容词作定语修饰mistake
表示可避免的错误

avoidal