The best answer to improve the effectiveness of the document above is C. adding a contact phone number and address to refer any questions.
This is because the document is asking the recipient to sign a contract, and it is important to make it easy for them to ask any questions they may have. By providing a contact phone number and address, the sender is making it clear that they are available to answer any questions and help the recipient understand the contract.
The other options are not as effective because:
A. attaching the contract in question is not necessary, as the recipient already has a copy of the contract.
B. listing the benefits of the contract is not necessary, as the recipient should already be aware of the benefits of the contract before they sign it.
D. including a small picture of the contract with the missing signatures highlighted is not necessary, as the missing signatures are clearly visible in the original document.
The best answer to improve the effectiveness of the document is C. adding a contact phone number and address to refer any questions. This is because it is important to make it easy for the recipient to ask any questions they may have before signing the contract.