4. A taxpayer whose gross income is less than his deductions and exemptions: a. has no tax due and can even claim a refund if too much income was withheld b. has no tax due, but is not entitled to a refund in that calendar year c. has no tax due, and must credit any withheld income during the year towards the next taxable year d. has no tax due, but must file a return in order to exempt himself from any statute of limitations on assessment