13. The contract comes into effect we can't go back on our word now.
合同现在生效，我们不能反悔了。
还能这样说：
The contract is effective now, we can't regret.
The contract begins to take effect and we can't go back on our promise.
应用解析：
in effect 正在实行，实际上；
come into effect 实行，实施；
put sth. into effect 使某物开始使用；
give effect to sth. 使某事物实行起来，使实施；
of no effect 没有预期或希望的结果，无效

14. Is the contract acceptable now?
合同现在可以接受了吗？
还能这样说：
Can you accept the contract now?
Are you ready for the contract?

15. All we have to do is to sign the contract.
我们要做的只是签订合同就行了。
还能这样说：
The only thing we need do is to sign the contract.
Signing the contract is the only thing we should do.
应用解析：
a sign of the times 时尚，潮流；
sign the petition 在请愿书上签字；
sign one's own death-warrant 做出可能使自己致命或失败的事

16. If the shipment can't be made within three months as stipulated, the contract will become void.
如果不能按原规定3个月内交货，合同则作废。
还能这样说：
The contract will be of no effect if you can't ship the goods within three months as stipulated.
If the shipment can't be made within three months according to the regulation, the contract will be to no avail.
应用解析：
void of sth. 没有某事物，缺乏某事物；
null and void 无法律约束力的，无效的

17. Once a contract is made, it must be strictly implemented.
合同一旦确定就应严格执行。
还能这样说：
On signing the contract, we should carry out it.
The signed contract must be executed strictly.
应用解析：
once for all 一劳永逸，永久地，彻底地；
once or twice 几次，一两次；
once upon a time 从前；
just this once 仅此一次，作为例外