In 1960, Grandfather GF Created a Trust with a Corpus

In 1960, Grandfather GF created a trust with a corpus of marketable securities worth $1 million.Under the terms of the trust instrument, GF's daughter D will receive the income from the trust as long as she lives.Upon D's death, the securities in the trust will be distributed to D's two children.Upon D's death in the current year, the securities had a market value of $5 million and were generating an average annual income to D of $400,000.Based on these facts, the amount includible in D's gross estate attributable to her interest in the trust is

A) $0
B) $400,000
C) $1,000,000
D) $5,000,000