Parent and Subsidiary Corporations Form an Affiliated Group

Parent and Subsidiary Corporations form an affiliated group.Last year,the initial year of operation,Parent and Subsidiary filed separate returns.This year,the group files a consolidated tax return.The results for last year and the current year are: Taxable Income
How much of Subsidiary's loss can be carried back to last year?

A) $0
B) $20,000
C) $25,000
D) none of the above