一般来说，买卖双方要签署书面合同作为达成协议的凭证和执行该协议的基础。

一般来说，买卖双方要签署书面合同作为达成协议的凭证和执行该协议的基础。

A written contract is generally signed by the seller and the buyer as the proof of the agreement and as the basis for its execution.