选b
首先,be afraid是没有be afraid doing sth的
只有be afraid to do sth 和 be afraid of sth/doing sth
be afraid to do sth,不敢去做某事
be afraid of doing sth,一向害怕做某事,表示习惯.
两者的区别,我写个例句就知道了.
she was not afraid of dancing with strangers,but she was afraid to dance with Mr.Green tonight,because she thought him dangerous.
她不害怕和陌生人跳舞（指在舞会上,表示习惯）,但是今晚,她不敢和格林跳舞（很可能格林向她发出邀请,因为她觉得格林是个危险人物,不敢跳舞只是今晚这一次）