第一句：Mr. Wang, I am sorry to tell you that we can't sign the contract with you next Monday.
王先生，很抱歉告知您我们不能在下周一和贵公司签署合同。
A: Mr. Wang, I am sorry to tell you that we can't sign the contract with you next Monday.
王先生，很抱歉告知您我们不能在下周一和贵公司签署合同。
B: The contract shall become effective as soon as it is signed by both parties.
只有两方都签订合同才能生效。
第二句：How about extending to two years and if things go smoothly, we can sign the contract next month.
如果事情进展顺利的话我们下个月就可以签署合同了。
A: When can you be right?
那贵方什么时候方便呢?
B: I am not sure.
不太确定。
A: This agreement will remain valid for one year.
这项协议一年内有效。
B: I am afraid we can't offer you the goods within one year. How about extending to two years and if things go smoothly, we can sign the contract next month.
恐怕我们不能在 一年内提供贵方所需的货物。延长到两年怎么样?如果事情进展顺利的话我们下个月就可以签署合同了。
其他表达法：
Any amendment of the contract shall come to force only after the written agreement is signed by both of us.
只有我们双方共同签署，合同的修改才会生效。
We'd like to make the contract to be valid for two years.
我们想让合同在两年内生效。
