under irc 673(a), the grantor of a trust is treated as the owner of a portion of that trust if he/she has a reversionary interest in either the principal or income of that portion of that trust if the value of the reversionary interest exceeded how much of the value of the portion in question at the inception of the trust?

1. 5%
2. 7.5%
3. 8.5%
4. 10%