A prophage is a Choose one: A. phage genome integrated into a host genome. B. bacterial virus particle that has not yet infected a cell. C. circular phage genome that promotes cell lysis. D. virus that promotes tumor growth in plants.

A. phage genome integrated into a host genome.

Explanation:

Virus reproduction is divided into two-cycle lytic cycle and lysogenic cycle. In the lytic cycle, viral DNA forms mRNA and produce capsid proteins which surrounds the viral genome and makes new phages that lyse the host cell.  

In the lysogenic cycle, the viral genome gets incorporated on the bacterial genome and replicates with the bacterial genome. This phage is called a prophage. So prophage is formed in lysogenic cycle and it does not cause lysis of the cell. Through this virus can multiply its genome. So the correct answer is A.