Question

i think he is clever 这个是宾语从句吗？为什么不用that引导？

Answer 1

that引导宾语从句时，通常情况下都可以省略that。例如：
He told me (that ）he would go to college the next year 　　他告诉我他明年上大学.
We all expect （that ）they will win,for members of their team are stronger. 　　
我们都预料他们会赢，因为他们的队员更强壮. 　　
He told us （that） they would help us through the whole work. 　　
他告诉我们在整个工作中，他们都会帮忙的.
I have found out （that） all the tickets for the concert have been sold out. 　　
我发现这场音乐会的所有票都卖光了. 　　
Can you work out （that）how much we will spend during the trip 　　
你能计算出这次旅行我们将花费多少钱吗

学习是一件愉快的事！ (*^__^*)
请及时采纳，多谢！

Answer 2

是的。that可以省略。

Answer 3

that可以省略的