What do metabolism, respiration, and digestion have in common?

They break larger molecules into smaller ones.

They build larger molecules.

They are each single chemical reactions.

They each involve multiple chemical reactions.

Metabolism, respiration and digestion are all complex chemical processes involving many steps, happening in 3 dimensional space within cells. Metabolism is the breaking of bonds within food molecules (like sugar) to harness energy for cellular work; respiration involves moving oxygen and carbon dioxide gases between cells to facilitate cellular metabolism and digestion involves breaking down food macro structures into smaller units suitable for metabolism.

So the answer is D - each of the three process involve multiple chemical reactions.