How would you most likely define "onerous" responsibilities?

The term "onerous" refers to something that is burdensome or oppressive, typically involving a significant amount of effort, difficulty, or hardship. When describing responsibilities as "onerous," it implies that these tasks require substantial commitment or exertion, making them heavy and demanding. This aligns perfectly with the choice that reflects the taxing nature of such responsibilities.

The other options present contrasting qualities; they suggest lightness or ease, which is not at all indicative of what "onerous" entails. Hence, the definition pointing to heavy and demanding responsibilities captures the essence of the word accurately.