Answer:
Carbon dioxide increases temperatures, extending the growing season and increasing humidity. Both factors have led to some additional plant growth. However, warmer temperatures also stress plants. With a longer, warmer growing season, plants need more water to survive.
Explanation:
Answer: New vaccines are offered each year because the virus changes.
Explanation: The flue viral strain constantly changes its genetic make up, a process called antigenic drift. As the virus replicates there are small changes that creates new strains which evolve to a completely different influenza virus requiring a new type of vaccine each year.
