In the oxygen–carbon dioxide cycle, a. animals produce oxygen used by plants for photosynthesis.
b. animals produce oxygen used by plants for respiration.
c. animals produce carbon dioxide used by plants for photosynthesis.
d. animals produce carbon dioxide used by plants for respiration.

C

Explanation:

Animals produce carbon dioxide as a byproduct of cellular respiration. Plants use the carbon dioxide through photosynthesis to produce oxygen.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

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what do the different brain waves do?

explanation:

brainwaves are produced by synchronised electrical pulses from masses of neurons communicating with each other. brainwaves are detected using sensors placed on the scalp. brainwave speed is measured in hertz (cycles per second) and they are divided into bands delineating slow, moderate, and fast waves.