16) Itch: ? :: Hunger: Eat
Hunger makes you want to eat something, and itch makes you want to scratch.
17) Computer: ? :: Human: Heart
CPU is known as the heart of a computer. As the heart is related to humans, a CPU is related to a computer.
18) Pacific: Ocean :: Greenland : ?
The Pacific Ocean is the largest ocean in the world, and Greenland is the largest island in the world.
19) Zoology: Animals :: Adenology:?
Zoology is the study of animals. Adenology is the study of glands.
20) Hypsiphobia: Height :: Hylophobia: ?
Hypsiphobia is the fear of heights, and hylophobia is the fear of forests.