A school has three classes in the morning, and there is a $$15$$-minutes break between each two classes. Each class is of the same length. The first class starts at $$9:45 $$, and the third class ends at $$12:00 $$. How long is each class? 
选项为:A:$$25$$  B:$$30$$  C:$$35$$  D:$$40$$  E:$$45$$  请回答其中一个选项.