Answer;
Primitive streak.
At the onset of the embryonic period, the primitive streak appears. It will eventually become the neural tube.
Explanation;
The primitive streak is a transient structure which forms on day 15 of human development.
It marks the start of gastrulation; the process in which the inner cell mass in converted into the trilaminar embryonic disc.
It originates from the anterior epiblast.
Answer:
1.—The (more) variations in forms it can produce.
2.—Biologists often need to search for evidence (in the distant past).
3.—By revealing the forms of (extinct species).
4.— (Intermediate) fossils can help biologists.....
Answer:
D. protists is the answer
The hydrogen bonding that created its hexagonal shape....the molecules get closer together and there will be more hydrogen bonding making it solid
