<span>D. A theory is backed up by repeated observations and tests.</span>
Answer:
365 million years ago
Explanation:
The tetrapods are a super-family which includes all living and extinct vertebrates that have walked and are still walking the Earth, including the mammals, reptilians, dinosaurs, sinapsids, pterodactyls, amphibians, birds. They have evolved from fish-like creatures that were living in the shallows, and over the course of millions of years they were slowly changing and adapting to amphibian life, thus partially aquatic, partially terrestrial. The first proper limbs, at least what is know so far from the fossil records, have emerged with the ichthyostega and acoantostega around 365 million years ago. These two species were able to lift their body above the ground with their limbs, support its weight, and walk on them without dragging their body on the ground. The first transitional limbs can be seen in a species that has been dated to around 375 million years ago, the Tiktaalik, which had had limbs, but still not well developed, and it was only able to stand on them while in shallow water, but on on land.
Passive trsansport bc they dont need energy to move thier molecule
