You are asked to conduct an audit by your client, namely PT A, which is engaged in book retail. According to the manager of PT A, the gross margin for the last 4 years has always decreased. The manager said that the drop was due to a drop in sales, as many people switched from buying books at bookstores to buying online. The following is PT A's data for the last four years:

	2017	2016	2015	2014
Sale (thousands)s	47,175	44,039	37,073	35,035
CoGS (thousand)s	30,314	27,998	23,431	22,072
Gross Margin $	16,861	16,041	13,642	12,963
Percent	35,7%	36,4%	36,8%	37%

as a financial auditor, you cannot just trust a statement from a manager. Perform vertical and horizontal analysis on the data above, to answer whether you agree or not with the manager's statement! Explain your answer!