Select the true statement.

rna is mostly single-stranded; dna is always double-stranded.
rna and dna usually have identical nitrogenous bases.
several types of dna regulate protein synthesis.

RNA is mostly single-stranded; DNA is always double-stranded.

Explanation:

DNA stores the genetic information that codes for the way protein should be developed by the cell. Protein determines the trait (phenotype) of the cell/organism. RNA is used as an intermediary between DNA and proteins.  RNA is made of ribonucleic acids  while DNA is made of deoxyribonucleic acids.

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explanation:

plate tectonics and volcanic euptions

over time, plate tectonic processes cause continents to move to different positions on the globe.

for example, britain was near to the equator 300 million years ago, and therefore was hotter than it is today. for further details look at our climate through time poster or online map.

the movement of the plates also causes volcanoes and mountains to form and these too can contribute to a change in climate.

mountain ranges formed by plate tectonics. large mountain chains can influence the circulation of air around the globe, and consequently influence the climate.   warm air might be deflected somewhere cooler by the mountains.

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.