That is a day never to be forgotten.(动词不定式的被动语态)
3. be+going to do，表示"打算或将要做某事"，be有现在和过去两种形式。如：
We are going to plant trees in the park.
I didn't know if she was going to come here.
4. be+to do，表示"按计划安排将要做某事"。如：
The new shop is not to be opened till next Monday.
One night an angel came to Mary and told her that she was to have this special boy.
功能三，there be
there be句式为：there be+主语部分＋状语部分，表示"某处存在某物"，be常用现在时，过去时和将来时等。如：
Oh, cool! And there are many things to see. There is even a deer park in Sanya.
There are about 80 pyramids in Egypt.
Will there be a football match in your school next week?
功能四，实义be
可以将be视为实义动词，因为它具有实际的词义，如"成为;做;发生;举行;逗留;到达"等。如：
His daughter wants to be a doctor for animals in her twenties.
Kate's birthday party will be at half past six this evening.
Jim has been in China for more than two years, but he has not yet been to Yichang.