Complete analogous pair - Deciduous : Willow : : Coniferous : ?

B. SPRUCE

Look at this series: 1.5, 2.3, 3.1, 3.9, . . .
What number should come next?

C. 4.7

Complete analogous pair - Coconut : Shell : : Letter : ?

D. ENVELOPE

Complete analogous pair - Hermit : Solitude : : Intruder : ?

C. BURGLAR

Complete analogous pair - Wine : Grapes : : Vodka : ?

D. FLOUR