Employees have begun to ____ about the company's recent tendency to frequently require overtime work, which has led to some physical exhaustion among them.A. congratulateB. complainC. negotiateD. anticipate

根据句意，空格处需填入一个能与“about”搭配的动词，表达“员工对频繁加班表示不满”。 - “congratulate”不符语境。 - “negotiate”不与“about”搭配。 - “anticipate”无法体现“开始……”之意。 - “complain”最贴切，可构成“complain about”，表示“抱怨……”。 最终，完整句子为： "Employees have begun to complain about the company's recent tendency to frequently require overtime work, which has led to some physical exhaustion among them."