這題是考對等連接詞的平行原則
Effective supervisors and understand the needs of their employees.
and 的後面是接「動詞 + 受詞」,所以可以判斷and連接兩個完整的句子,只是第二句的主詞重複省略掉而已,所以原句是
Effective supervisors know their work thoroughly and (effective supervisors) understand the needs of their employees.
24. Effective supervisors __________ and..-阿摩線上測驗