&nbsp;&nbsp; &nbsp;You have received different service requests for the Products that have been sold by a company for a data entry task. Which of the following can be recorded as a unique identifier for different service requests?<br />
a) Customer&rsquo;s last name &nbsp; &nbsp; &nbsp; &nbsp;<br />
b) Customer&rsquo;s first name &nbsp; &nbsp; &nbsp;&nbsp;<br />
c) Customer&rsquo;s age &nbsp; &nbsp; &nbsp;<br />
d) Invoice number