Answer:
Gas exchange during respiration occurs primarily through diffusion. Gas molecules move from a region of high concentration to a region of low concentration. Blood that is low in oxygen concentration and high in carbon dioxide concentration undergoes gas exchange with air in the lungs.
Explanation:
A) gravitropism is how they "know"
HOW IS YOUR DAY AND THE ANSWER IS B BY THE WAY AND I HOPE I HELPED BYR
That is not the correct answer