Are reactants in the process of cell respiration.
water and sugar
sugar and oxygen
water and oxygen
water and carbon dioxide

sugar and oxygen

Explanation:

As it turns out, oxygen is the essential ingredient for making energy in a process called cellular respiration. ... All body cells engage in cellular respiration. They use oxygen and glucose, a sugar found in the foods we eat and convert them to ATP (adenosine triphosphate), or cellular energy, and carbon dioxide.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.