Question $18(2\mathrm{.}75$ points$)$

Which of the following Regulations deals with estate taxes?

Reg. $$20\mathrm{.}2503-4$

Reg. $$1\mathrm{.}6662-5T$

Reg $$1\mathrm{.}162-21(a)(2)$

Reg. $$31\mathrm{.}3121(a)-(2)$