Points $A$ and $B$ are 10 units apart. Points $B$ and $C$ are 4 units apart. Points $C$ and $D$ are 3 units apart. If $A$ and $D$ are as close as possible, then the number of units between them is ．(1996 AJHSME, Question 8) 
选项为:A:$$0$$  B:$$3$$  C:$$9$$  D:$$11$$  E:$$17$$  请回答其中一个选项.