That is true
Hope this helps
Scientists are creating vaccinations that prevent people from getting bird flu. If the virus mutates, a new vaccine needs to be made. The vaccine needs to be tested, which can be dangerous. It also takes a long time for scientists to know whether the vaccine works.
Answer: digestive and excretory completes the sentence.
As long as calories consumed and expended are not the same, diet or activity level should be adjusted for the good of the body's health.
