Which, if any, of the following items characterizes the election to defer Federal estate tax payments relative to an interest in a closely held business?

a. The estate tax is paid over the last 10 years or less.
b. Interest must be paid during the complete deferral period.
c. Interests in closely held businesses can be aggregated only if the 20% ownership test is satisfied.
d. For 2017, the 2% rate applies only to the first $1,490,000 in estate tax value.