Sentence:  If your principal place of abode for the tax year is outside the United States ( including Alaska and Hawaii ) , Puerto Rico , or the Virgin Islands and you have no legal residence or <WSD>principal</WSD> place of business in any internal revenue district in the United States , you should file your return with the Office of International Operations , Internal Revenue Service , Washington 25 , D. C. . 
Meaning of the word marked with <WSD> tags:  most important element