It is 200 million years because it has been around for a long time.
Answer: Four pulmonary veins.
Explanation: Oxygen and nutrient rich blood will flow from the lungs back into this part called the left atrium (Or as some will call it, the left upper chamber in the heart). From there, it goes through four pulmonary veins.
Hope I could help! :)
Answer:
uhh either natural and reproductive pretty sure it's reproductive
Answer:
1. Precambrian rocks are very old.
2. They have very few fossils.
