她为她的论文辩护到底。

She defended her thesis ___to ___the ___bitter ___end.

他们将抗议到底以保护环境。

They will protest ___till ___the ___bitter ___end to protect the environment.

他坚持比赛直到最后，尽管受伤了。

He stayed in the game ___until ___the ___bitter ___end, even though he was injured.