Can you clarify your question; what section are you in where you are asked this question? I am not sure what you are referring to, so can you send a screenshot (without any personal info) or provide more details?
By default your income and tax withholding are treated as received and paid uniformly throughout the year. However, you might have had a large item of income in the 4th quarter of the year and did not have enough taxes withheld to sufficiently cover the tax liability to avoid an underpayment penalty for earlier tax quarters unless you make an estimated tax payment and annualize income. Annualizing income puts your Q1 income entirely in Q1, but with the default treatment of tax withholding as paid uniformly throughout the year you end up with only a portion of your tax withholding credited to Q1. This results in a tax underpayment for Q1. Treating the withholding as paid when withheld credits all of the tax withholding as paid in Q1 to cover the Q1 income.