请你根据句意及所给汉语提示，写出单词的正确形式。
1.I'll buy a ________ for my mother's birthday. (礼物)
2.You can't drive a car if you don't have a driver's _________. (证件)
3.There is no _________ between you and me, right? (秘密)
4.I won't go there _________ you go. (除非)
5.It's _________ for you to get enough sleep every day. (有必要的)
