固定短语be lost in thought，例如：
1、He was nearly hit by a car for being lost in thought.
2、I didn't answer right away because I was lost in thought.我陷入沉思了没有回答到点子上。
3、1The old man was lost in thought and did not hear us come in.这个老人凝神沉思，没有听见我们进来。
thought固定短语
是at the thought of ，中文意思是，一想起，一想到
I was full of joy at the thought of seeing my best friend again.一想到要能再次与我最好的朋友见面，我就满心欢喜。
She was overwhelmed with fear at the thought of what she had done.
一想到自己所做的事，她就感觉非常害怕。
