Correct Answer: Scheme

Solution : The correct choice is the second option.

The most appropriate synonym for the word proposal is scheme. A proposal is a suggestion or plan presented for consideration, and a scheme shares a similar essence in proposing a plan or arrangement for a specific purpose.

The meanings of the other options are as follows:

• Filling refers to putting something into a space or container to make it full.
• Refusal refers to the act of denying or rejecting something.
• Addition refers to the act of adding something to something else, usually to increase its size, number, or amount.

Therefore, the correct answer is scheme.