On December 5, 2019, Triad Corporation invested $500,000 in short-term available-for-sale marketable securities. The market value of this investment was $550,000 at December 31, 2019, but had slipped to $525,000 by December 31, 2020. (I). Assuming Triad Corporation does not sell this investment, the mark-to-market adjustment necessary at December 31, 2020, includes: Select one: O a. A $25,000 credit to unrealized gain/loss on Investments b. A $25,000 debit to unrealized gain/loss on Investments. Oc A $525,000 debit to Investments in Marketable Securities, d. A $25,000 debit to Investments in Marketable Securities