To make a valid contract, generally speaking, we need at least two parties;

一般而言，为订立一份有效合同，至少需要两方当事人；

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To create a valid contract an offer must be accepted without qualifications.

只有毫无保留地接受要约才能成立一个有效的合同。

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A sales order becomes a valid contract, only if it is confirmed in writing by WIRTGEN CHINA.

仅在WIRTGEN CHINA书面确认的情况下，销售定单方能构成有效的合同。

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The club appealed against their punishment, claiming that Kakuta did not have a valid contract with the French club.

BBC: Chelsea's Gael Kakuta secures Fulham loan move

Entrants may only register a mobile phone for which they have a valid telephony contract.

CNN: Euro 2008 SMS Alerts Terms & Conditions

All the players bought from the auction in Mumbai will be given a one-year contract valid until 31 December which will also cover a Champions League Twenty20 tournament later this year.

BBC: Eoin Morgan seals Bangalore IPL deal