There are $15$ floors in a building, and every two floors have the same number of stairs. They tell us that person $A$ goes up the stairs twice as fast as person $B$, so they both start on floor $1$, and when person $B$ gets to floor $6$, which floor is Person $A$ on? 
选项为:A:on the $11$th floor  B:on the $12$th floor  C:on the $8$th floor  D:on the $6$th floor  E:on the $7$th floor  请回答其中一个选项.