我有两道练习题，请帮忙解答一下

1.which income statement colimnsof the extended trial balance should the balance for sales return and purchase be extended ?

A debit debit  B debit credit   C credit debit D credit credit

2.after completing final acounts ,the compay found that their understrated a prepayment .

how are the company's net profit and capital affected by the correction of the error ?

A increased increased   B increased decreased   C decreased increased  D decreased decreased

请帮忙解答 ，最好能具体一点  万分感激