单项选择题

It is claimed that horse racing was at first the most common outdoor amusement.

A.据说赛马最初是最平常的户外娱乐活动。
B.有人说最初最平常的户外娱乐活动是赛马。
C.有人主张赛马最开始应该是户外娱乐活动。
D.听说赛马最初是最普遍的户外娱乐。