The umbra is the innermost and dark part of the shadow where like it’s created by any light source and is completely blocked by the occluding body. It’s a Latin term hope this helps man!
Embryologist study embryos because Embryology is central to evolutionary developmental biology ("evo-devo"), which studies the genetic control of the development process (e.g. morphogens), its link to cell signalling, its roles in certain diseases and mutations, and its links to stem cell research.
B. I think I'm not so sure but that's my best guess.