是n. 先锋拓荒者（pioneer 的复数），v. 当先锋为……开路（pioneer 的三单形式）

We were welcomed by the smiles on the faces of many young pioneers.我们受到了许多满脸笑容的少先队员的欢迎。

He wanted them to learn from those great pioneers of America.他希望他们向美国那些伟大的拓荒者学习。