那是的用法和样例：
例句
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那是一段艰难的日子。
That was a hard time. -
我喜欢回顾我的中学时代，那是我生命中最快乐的时光。
I like to look back on my high-school days, which were the happiest in my life. -
电视台为出现的干扰表示歉意，那是由于恶劣的天气状况造成的。
The television station apologized for the interference, which was due to bad weather conditions. -
那是一个以几种语言叙述的古老的故事。
It's an ancient tale which appears in various guises in several languages. -
那是我的两个儿子。你能猜出哪个大吗？
There go my two sons. Can you guess which is the elder?
