Why do astronauts need to be concerned about EM waves in outer space?

Which phrase is most likely to start a description of a scientific theory? “what i have found through my online research is . .” “after much thought, i believe that the best explanation is . .” “based on the observations made and experiments performed over the last fifty years . .” “if sunlight shines on the right side of a plant, then the plant will grow toward the right because . .”

Which best describes the digestive system of arthropods? a incomplete, two openings b complete, one opening c two-way, one opening d one-way, two openings

Aperson with age is more likely to catch diseases that healthy people usually don’t catch.what are these infections called?