Answer:
The correct answer to the question: The diagram shows the process of a transcription, which takes place in the nucleus of a cell. What is occurring?, would be, B: DNA is being used as a template to make a molecule of mRNA.
Step-by-step explanation:
The answer comes from learning about the process of transcription, or genetic transcription, whose ultimate purpose is to transcribe the information present inside the DNA of a cell´s nucleus, to form proteins that will be the ones to execute the functions in the organism. During this process of transcription, the RNA polymerase opens up the DNA strand, and starts to "read" the DNA sequences, copying it exactly into an mRNA strand, which will be responsible for carrying the genetic message so that a new protein can be generated.