a valid argument/criticism/reason
令人信服的論據/批評/理由
My way of thinking might be different from yours, but it's equally valid.
我的想法也許和你的不同,但同樣站得住腳。
My passport is valid for another two years.
我的護照還有兩年有效期。
Is this contract/ticket/agreement still valid?
這份合同/這張票據/這份協定還有法律效力嗎?