Complete analogous pair - Snake : Fang : : Bee : ?

D. STING

Complete analogous pair - Oasis : Sand : : Island : ?

C. WATER

Complete analogous pair - Melt : Liquid : : Freeze : ?

C. SOLID

Complete analogous pair - Pituitary : Brain : : Thymus : ?

D. CHEST

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

C. 4.7