一群海豚用英语怎么说？

一群海豚

a school of dolphins

school

n. 学校，上学，学院，群；vt. 训练，锻炼，教育，教导，约束，给…上学；

例句
I was terrible at school and left with few academic qualifications...
我的学习成绩一塌糊涂，离校时几乎没有学历。

of

prep. 关于，属于…的，由…制成；aux. 助动词 [非标准用语、方言] =have [主用于虚拟语气]；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

dolphins

n. 海豚（ dolphin的名词复数 ）；

例句
Many dolphins are accidentally killed through entanglement with fishing equipment.
很多海豚因为被渔具缠住而意外死亡。