$($LO $4\mathrm{.}4)$ According to Porter's five forces, the fact that vendors requiring quick payment or cash payment from their customers may indicate the power of which of the following and may have what impact on the accounts receivable turnover?

a$.$ Vendor power and faster accounts receivable turnover

b$.$ Customer power and faster accounts receivable turnover

c$.$ Vendor power and slower accounts receivable turnover

d$.$ Customer power and slower accounts receivable turnover