The correct answer is D. Electromagnetic
Step-by-step explanation:
Electron and protons are both subatomic particles that differ in their mass and other features including electromagnetic charges. Indeed, protons are positively charged, while electrons are negatively charged. This difference in electromagnetic charges causes electrons to be attracted to electrons, and vice versa due to electromagnetic forces as particles with different charges attract each other while those with the same charges repel each other. Thus, an electron and a proton attract each other as a result of electromagnetic forces.