Choice "D" is correct. An involuntary petition for bankruptcy can be filed if a debtor owes more than $15,325 in unsecured debt and is not paying its debts as they become due.
Choice "a" is incorrect. The debtor must owe at least $15,325 to all of the unsecured creditors. There is no requirement that one creditor be owed any specified amount.
Choice "c" is incorrect. There can be more than 12 creditors. If there are more than 12 creditors, at least 3 must join together in filing the petition.
Choice "b" is incorrect. There is no requirement that a secured creditor join in the petition.