Question

evolution can happen in...

a single bacterial cell
a frozen sample of cells
a strain of flu virus spreading in a population
a population with no genetic variation

Explanation:

Evolution is a change in the genetic composition of a population over time. A single bacterial cell or a frozen sample of cells do not have the necessary population - level genetic changes for evolution. A population with no genetic variation cannot undergo evolution as there is no material for natural selection or other evolutionary forces to act on. However, a strain of flu virus spreading in a population can experience genetic changes (such as mutations) and changes in allele frequencies as it spreads and interacts with the host population, which is in line with the concept of evolution.

Answer:

a strain of flu virus spreading in a population