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Mice develop as embryos inside their mother and undergo live birth. The following illustration shows an adult mouse.

A mouse with white fur. The mouse has a head, eyes, a tail, four limbs, fingers, toes, ears, a snout, and whiskers.
The next three illustrations show mouse embryos. Each one is in a different stage of development. The illustrations are not drawn to scale.
Of the three embryos, which one is in the EARLIEST stage of development?
Choose 1 answer:
Choose 1 answer:
(Choice A) A mouse embryo with a spinal cord, a head, eyes, a tail, and limbs.
A
A mouse embryo with a spinal cord, a head, eyes, a tail, and limbs.
(Choice B) A mouse embryo with a spinal cord, a head, eyes, a tail, limbs, fingers, toes, ears, and a snout.
B
A mouse embryo with a spinal cord, a head, eyes, a tail, limbs, fingers, toes, ears, and a snout.
(Choice C) A mouse embryo with a spinal cord.
C
A mouse embryo with a spinal cord.

1 answer

The embryo in the EARLIEST stage of development would be the one with the least developed structures.

  • Choice A has a spinal cord, head, eyes, a tail, and limbs.
  • Choice B has a more developed set of features, including fingers, toes, ears, and a snout in addition to the features in Choice A.
  • Choice C only has a spinal cord, indicating it has the least amount of development compared to the others.

Therefore, the embryo in the EARLIEST stage of development is:

(Choice C) A mouse embryo with a spinal cord.