Correct: The sun is the center of the solar system. It is mostly gas. It is the most massive object in the solar system.
The correct answer is phosphorylation. When an ADP (Adenine Diphosphate) molecule gains a phosphate, it becomes an (Adenine Triphosphate) molecule. This process is called a phosphorylation. Phosphorylation and its counterpart dephosphorylation change many proteins in terms of its functions and activities.