The reason you were asked that question is that special rules apply if you are out of the country on April 15th. If this does not matter to you, then the blank would be acceptable.
From the IRS:
Taxpayers who are out of the country. If, on the regular due date of your return, you’re out of the country and a U.S. citizen or resident, you’re allowed 2 extra months to file your return and pay any amount due without requesting an extension. Interest will still be charged, however, on payments made after the regular due date, without regard to the extension.
More information from the IRS:
https://www.irs.gov/pub/irs-pdf/f4868.pdf
