The Setting Every Community Up for Retirement Enhancement (SECURE) Act modified the tax rates and brackets that the taxpayer will use to figure the Tax for Certain Children Who Have Unearned Income (Kiddie Tax) on his or her 2021 unearned income. Under the SECURE Act, all a child's net unearned income over a threshold amount is taxed using the brackets and rates for which of the following?

A. Capital gains

B. Child's parents

C. Estates and trusts

D. Partnerships