There are $6$ boxes each contains only oranges, apples, or pears. The boxes weigh $$15$$, $$16$$, $$18$$, $$19$$, $$20$$, and $$31$$ kg, respectively. If the total weight of apples is half of that of pears, and there is only one box of oranges, what is the weight of the box of oranges. 
选项为:A:$$15$$  B:$$18$$  C:$$19$$  D:$$20$$  E:$$31$$  请回答其中一个选项.