请根据句意从方框中选用合适的单词，并用其适当形式填空，使句子通顺。

they    ninety    little   invent    usual

Simon and Linda looked at each other and kept their secret to ___________.
This is really an _________ experience. I will never forget it.
Grandma’s ____________ birthday is coming. We are going to hold a party at her home.
Computer is one of the greatest _____________ in the world. I can’t imagine what life is like without it.
Of all the students, our monitor spent the ___________ time but made the most progress.