我知道你今天有很多事情要做。
wǒzhīdào nǐ jīntiān yǒu hěnduō shìqíng yào zuò 。
I know you have many things to do today.
你知道他为什么没有来吗?
nǐ zhīdào tā wéishènmǒ méiyǒu lái ma ?
Do you know why he didn't come?
我知道这个问题的答案。
wǒzhīdào zhègè wèntí de dáàn 。
I know the answer to this question.