Which summary best explains the mechanisms that control the cell cycle in multicellular
organisms?
the type of dna in each cell controls the rate of the cell cycle and the specific type of cells
formed
the size of the cell determines the number of cells that will be produced from each cycle.
internal and external signals regulate the progression of the cell cycle at various critical
checkpoints
hormones signal the start of the cell cycle, and dna determines how the cell differentiates.

The correct answer is internal and external signals regulate the progression of the cell cycle at various critical check points.

Explanation:

The cyclic event that helps to prepare the cell for division is termed as cell cycle.Cell cycle are regulated by various internal and external factors which regulates the passage of cell through various critical check point.

 For example Maturation promoting factor helps in the progression of frog egg oocytes cells from G2 to M phase.

    G1 cyclin CDK helps in the passage of cell from G1 to S phase.

the national environmental policy act (nepa) is a united states environmental law that promotes the enhancement of the environment and established the president's council on environmental quality (ceq). the law was enacted on january 1, 1970. to date, more than 100 nations around the world have enacted national environmental policies modeled after nepa.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."