thought

n. 想法,思想
v. (think的过去式和过去分词)想,思考,认为
vbl. 想,思考,认为

The 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。

What's the central thought of this article?

这篇文章的中心思想是什么？