她对丢失文件给出了一个不太可信的解释。

She offered an ___unlikely explanation for the missing documents.

这是一个涉及时间旅行和外星人相遇的不太可信的故事。

It's an ___unlikely tale involving time travel and alien encounters.

鉴于他的背景，他自称是特工的说法似乎极不可能。

His claim of being a secret agent seems highly ___unlikely given his background.