Lawrence owns the following assets. All assets, except for one, are included in his gross estate and probate estate at death. Which asset is not included in his probate estate?

a. A promissory note Lawrence held on the sale of his business for $400,000

b. A vacation home Lawrence owned in a state other than his state of residence

c. A life insurance policy Lawrence owned on his life that is payable to his estate

d. An irrevocable trust that Lawrence created five years ago and funded with $500,000. Lawrence named himself trustee and retained the right to change the trust beneficiaries.