If memory cells are always present after the first exposure to a virus, then why do people get the flu every year?

In which specialized organ of the plant would these cells most likely be found

What type of specimens where you able to see under each of the microscopes in the microscope activity

Which would best keep the oxygen cycle stable? a. cutting down jungles to create farmland b. eliminating parks in large cities c. dumping toxic chemicals into the ocean d. reducing the amount of deforestation d. reducing the amount of deforestation