How many years ago did flowering plants evolve?

3.5 billion

144 million

50,000

5,000

Why can influenza viruses reinfect a person even after memory cells have produced immunity?

The most common isotope of oxygen has atomic number 8 and atomic mass number 16. another isotope has two extra neutrons. what are the atomic number and atomic mass number of this isotope?

The trachea and bronchial tree can be seen with an instrument called

What happens during cellular respiration

Which statement best relates science and societal problems? A. Societal problems are the result of science. B. Any societal problem can be solved by using science. C. A scientific solution to a societal problem does not result in further problems. D.

The table above shows five different types of chromosomal abnormalities that can occur during meiosis. They result in either an individual having too many or too few chromosomes in their genome.

During which stage of disease should an infected person be considered contagious

A scientist observed the boundrary between teo tectonic plates for a decade and finds that no new volcanoes have formed over the course of her investigation. Does this result suppor the theory of plate tectonic? Why or why not?

Do you think the channel on Mars was formed by flowing water or flowing lava

Does the presence of acid-fast organisms in a clinical specimen always suggest serious clinical disease? why or why not?