Climb as ------ as the top of the hill,and you may find the

选D
去到有多远的距离用far不用long,如：How far is it from you home to your school?你家离学校有多远?
the entrance/exit of a place（地方的出入口）,the answer to the question（问题的答案）,the key to he lock（锁的钥匙）这类的所有格要用to,不用of