$5\mathrm{.}36$ Consider the ball$-$and$-$stick models A$-$D$.$ How is each pair of compounds related: $($a$)$ A and B; $($b$)$ A and C; $($c$)$ A and D; $($d$)$ C and D$?$ Choose from identical molecules, enantiomers, or diastereomers.

A

B

C

D