The Otto cycle used to model the four-stroke gasoline engine is drawn as a closed loop on a pressure-volume diagram with four paths: AB, BC, CD and DA. According to the source, what two kinds of thermodynamic processes make up this cycle?

1. In the Otto cycle, paths AB and CD correspond to the nearly adiabatic compression and power strokes, so both of these legs are adiabatic processes with no heat transfer. 2. Paths BC and DA occur at constant volume, corresponding to the ignition and exhaust-intake portions of the engine's cycle, making both of these legs isochoric processes. 3. This combination of two adiabatic and two isochoric legs is exactly what makes up the Otto cycle, ruling out option A's four isobaric legs and option D's four isothermal legs. 4. Option B mixes in isobaric and isothermal legs, neither of which appears anywhere in this particular cycle. _Source: OpenStax College Physics (CC BY 4.0), Ch 15 "Thermodynamics", section 15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency_