I believe that the answer to this question is A. Demand for cheap, processed food.
When the egg cell is fertilized with the sperm cell, it changes into a zygote. It then becomes a morula and blastula. Then it turns into grastula and neurula where neural plate is transformed into neural tube.. Finally, it becomes a human embryo.
The tool that Carl will need in order to conduct his experiment is a thermometer.
The end of a difficult time (aka hope )