that引导的宾语从句是并列句,第二分句前that可省吗?可以说个句子细细讲解吗?

当一个动词带有两个或两个以上宾语从句时,此时第一个that可以省略,第二个that不可以省略;
例如 Then he said that Chinese was one of the most difficult languag in the world and that we must keep it among us and practice it every day.

当宾语从句不止一个时,第一个that 可省略,而其他的that不能省.
I think (that)it will clear up this afternoon and that they will come to say goodbye to us.
我认为今天下午天会放晴,他们会来向我们告别.