In this park,birds often fly down from trees to eat from visitor

In this park,birds often fly down from trees to eat from visitor’s hands.They are used to ______ in this way.
A、be fed
B、feed
C、having fed
D、being fed
【正确答案】：D
【题目解析】：be used to doing 习惯做某事，They are used to being fed this way他们习惯被这种方式喂食