How are waste products in the blood removed from the body?

Several billion years ago which gas was the least prevailant in the atmosphere

Which of the following is a period in the paleozoic era? devonian cambrian permian all of the above

Which one is an advantage of external fertilization a. the offspring are genetically identical to the parents b. more eggs can be fertilzed at one time c. more sperm can be released at one time d. more protection is available for developing plz