In Which, If Any, of the Following Independent Situations Can

In which, if any, of the following independent situations can the alternate valuation date be elected? $\begin{array}{cccc}&\text { Value of Gross Estate }&&\text { Estate Tax Result }\\&\text { Date of Death } & \text { Alternate Date } & \text { Date of Death } & \text { Alternate Date } \\a.&\$ 6,000,000 & \$ 6,100,000 & \$ 400,000 & \$ 390,000 \\b.&\$ 5,900,000 & \$ 5,800,000 & \$ 400,000 & \$ 405,000\\c.&\$ 6,100,000 & \$ 6,000,000 & \$ 390,000 & \$ 380,000 \\d.&\$ 6,200,000 & \$ 6,300,000 & \$ 500,000 & \$ 490,000\\\end{array}$