Final answer:
The correct synonym for 'effortless', in the context of graceful movement, is 'smooth'. 'Strenuous', 'arduous', and 'laborious' imply effort, so they are not correct synonyms for 'effortless'.
Step-by-step explanation:
The word 'effortless' describes an action done with ease and without the need for hard work. In the context given, a synonym for 'effortless' that describes movement in a fluid and easy way is 'smooth'.
Here is why each option stands in terms of its synonymy with 'effortless':
- Strenuous, arduous, and laborious all imply a task that requires a lot of effort and therefore are antonyms of 'effortless'.
- Smooth, on the other hand, implies being even and easy, often associated with a lack of difficulty or effort, making it the correct synonym in this context.