The atmosphere contains a large amount of nitrogen in a form that cannot be used by plants and animals. Which is a form of nitrogen that plants and animals can use.
A. Trees convert nitrogen into bacteria which makes it useful
B. bacteria release nitrogen into the atmosphere
C. bacteria change nitrogen into nitrates
D. animals fix nitrogen into ammonia which is used by plants

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.

evidence and logical support is essential for a scientist to do in order to maintain credibility. this is because no one can believe without any logic and without any evidence.hence a scientist can maintain credibility by proving himself and by answering logically so experiments prove very beneficial. logical hypothesis give conclusion which is acceptable. therefore, there are two main factors to maintain credibility by a scientist is evidence and logical support.