A hydrangea plant has blue flowers when grown in acidic soil, but has pink flowers when grown in basic soil. A clone of the pink-flowered plant is grown in acidic soil and produces blue flowers. This change in flower color is most likely due to:

A. sexual reproduction in the plants, resulting in variation
B. asexual reproduction in the plants, resulting in variation
C. genes being expressed in different ways due to environmental conditions
D. a gene mutation that occurred after the clone was produced