Which condition is required for viruses to reproduce? they must enter another virus structure. they must enter the cell of another organism. they must come in contact with water. they must encounter a virus with genetic material different from their own.

They must enter the cell of another organism.

Explanation:

Viruses are intracellular parasitic organisms. It posses genetic material in the form of ribonucleic acid (RNA) which is enclosed inside a protein envelop. A virus being a parasite invade a host organism cell to produce it's own progeny viruses. A virus attach itself to the specific receptor site on the host cell membrane. The protein coat is left outside the cell and the viral genetic material is injected inside the host cell. Then replication of the viral genome takes place inside the host genome. The progeny viruses release from the host cell machinery by lysis of the host cell.

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.

the answers are a and c