Final answer:
To determine if a plant reproduces sexually or asexually, a scientist should ask how the plant's genetic makeup compares to its offspring (Option C). Asexual reproduction results in identical offspring genetics, while sexual reproduction leads to a combination of genes from both parents.
Step-by-step explanation:
To determine whether a newly discovered plant reproduces sexually or asexually, the scientist should ask the question: How does the genetic makeup of the plant compare to its offspring (Option C)?
If the plant reproduces asexually, the offspring will have a genetic makeup that is identical to the parent, barring mutations. For plants that reproduce sexually, the genetic makeup of the offspring will be a combination of the genetics from both parent plants due to the fusion of gametes (sperm and egg cells in plants). Therefore, examining the genetic similarity between the parent plant and its offspring can provide insights into the plant's mode of reproduction. Questions about chromosome number or cell count would not directly answer how the plant reproduces, and the lifespan of the plant is unrelated to the type of reproduction.