Which of the following gases were present in the atmosphere of 4 billion years ago?

A) water

B) methane

C) ammonia

D) all of the above

Which marine ecosystem has the fewest available nutrients and the lowest productivity

3 properties of ultraviolet rays

What is an example of stablizing selection

If the epiglottis fails to close correctly over the trachea when a person swallows what will most likely happen? A. The person may experience heartburn. B. The person may choke. C. The person will experience a heart attack. D.

Which of these demands leads to more land being used for farming than is necessary to feed the human population? A. Demand for cheap, convenient food B. Demand for a meat-based diet C. Demand for fresh produce year-round D. Demand for processed food

Why did mendels use characteristics that only had 2 options? how did this aid in the development of his theories?

8. Modern fishing practices threaten biodiversity mainly through the

What is transpiration, and how does it occur within a plant

Describe each of the four mechanisms that cause air to rise.

Can a solution have a color?