You use mostly to indicate that a statement is generally true, for example true about the majority of a group of things or people, true most of the time. 主要地; 大多地
adverb [程度副词]多半,主要地;几乎全部,几乎所有、大多数
I am working with mostly highly motivated people. 我正与大多都积极性很高的人们共事。