The fast spread of diseases is due to the lack of hygiene, the poor salubrity in public spaces, and the contamination of food and water.
Climate change is mainly due to the high concentration of greenhouse gases, and those in high concentrations have demonstrated adverse effects on health.
The fact that drugs are getting less effective in stopping the spread of diseases, and eradicating them, also makes the disease harder to control. And also, some mutations of the microbes can contribute to their ability to infect, and therefore spread the disease.
All of the factors contribute to the harder control of diseases, and might as well help them to spread. Therefore, the answer is A.