Other things held constant, which of the following will cause an increase in net working capital?

Other things held constant, which of the following will cause an increase in net working capital?

a.Cash is used to buy marketable securities.

b.Supplier of raw materials gives 30 more days for payment.

c.Merchandise is returned and a refund is given.

d.Long-term bonds are retired with the proceeds of a preferred stock issue.

e.Missing inventory is written off against retained earnings.