- The children played happily under the tree.
- Happily played the children under the tree.
- Under the tree happily played the children.
- Under the tree, played happily the children.
The correct sentence structure in English is Subject-Verb-Adverb-Object. The subject (the children) should be followed by the verb (played), then the adverb (happily), and finally, the object (under the tree). The correct option (a) follows this structure.
