a flock of pigeons的用法和样例：
- A flock of pigeons fluttered down on to the grass in front of them and began strutting about, stopping now and then to cock their heads on one side and look at the young couple.
- A flock of sheep poured through the gate.
- This time I looked outside myself and noticed some children feeding a flock of pigeons couples waltzing under the trees the old man pushing his friend in a wheelchair.
- In the forest, we came upon a flock of pheasants.
- We saw a flock of geese swimming in the lake.