Sentence:  ( 1 ) your reasons for requesting an extension , ( 2 ) whether you filed timely income tax returns for the 3 preceding years , and ( 3 ) whether you were required to file an estimated return for the year , and if so whether you did file and have paid the estimated tax payments on or before the <WSD>due</WSD> dates . 
Meaning of the word marked with <WSD> tags:  the date on which an obligation must be repaid