5. We think your draft contract needs some modification.
我方认为贵方草拟的合同需要做一些修改。
还能这样说：
We feel that the contract you made needs to be revised partly.
We think we should modify the contract in some respects.
应用解析：
make out a draft of 起草；
on draft 桶装的，随时可以从桶里汲出的

6. Once a contract is signed, it has legal effect.
合同一旦签署即具有法律效力。
还能这样说：
This contract will come into force as soon as it signed by two parties.
A contract become valid immediately after it is signed.
应用解析：
be in force 生效，有效；
be forced into 被迫；
bring into force 使生效，实施

7. The buyer has the option of canceling the contract.
买主有权撤销合同。
还能这样说：
The buyer has the right to declare that the contract is null and void.
The buyer has the final say on repealing the contract.
应用解析：
at sb.'s option 随某人的意；
keep (leave) one's options open 暂不表态，留有回旋余地

8. We can get the contract finalized now.
现在我们可以签订合同了。
还能这样说：
We can sign the contract now.
It's time to reach the agreement now.
应用解析：
finalize the design 定型；
finalize model 最终确定模型