Answer:
c. Appeal to the receiver's sense of responsibility and pride in the company's good name.
Explanation:
Mikhail has already claimed once, and that he did not receive the rebate package, which was promised to him by the digital company.
Generally, companies these days while making deals on internet offer certain rebates. Sometimes these are not provided at the time of placing order, rather it is made as a rebate when goods are delivered or etc:
He shall then after making the first mail, he shall make a second mail, describing the responsibility of the company for such rebate and then asking for the same as the company has a good reputation which shall be maintained.