Opula Inc. is a company that designs jewelry. It needs secondary data to know its customers' preferred jewelry patterns. In this scenario, which of the following secondary data can Opula Inc. obtain from within the firm?

a$.$ Summaries of income data of all jewelry businesses compiled by the state and federal agencies

b$.$ Articles published in reputed business magazines about Opula's profit margins

c$.$ Data published by trade associations dealing with the recent jewelry market strategies

d$.$ Social media posts entered by Opula's customers on its trending jewely designs