18: D, homologous
20: B, DNA
I can’t see 17 or 19!
The first living things on Earth, single-celled micro-organisms<span> or microbes lacking a cell nucleus or cell membrane known as prokaryotes, seem to have </span>first<span> appeared on </span>Earth<span> almost four billion years ago, just a few hundred million years after the formation of the </span>Earth<span> itself.</span>
Answer:
Explanation:
Alkali metals (rarely 'Hydrogen and the alkali metals')
Alkaline earth metals (in old chemistry this name applied only to Ca and its congeners)
Icosagens (unofficial name; aka Boron group; rarely Earth metals)
Crystallogens (unofficial name; aka Carbon group; rarely Adamantogens[a] or Merylides[b])
Pnictogens
Chalcogens
Halogens
Noble gases (rarely Aerogens). The Group name may have to be changed to the “Helium group” since oganesson is not expected to be noble.
A seals flippers has finger bones when a birds wing is just a bone connected to other joints.
