There are $20$ balls of the same size in a box.  Lucas says: "$\frac12$ of them are red."  Peter says: "The probability of drawing a green ball without observing them is $\frac15$."  Claire says: "There are three colors of balls in the box: red, light blue, and green."  How many dark blue balls are there in the box? 
选项为:A:$$0$$  B:$$4$$  C:$$5$$  D:$$6$$  E:$$10$$  请回答其中一个选项.