The girl happily ate rice.

Meaning: This means that a specific girl is eating rice and she is feeling very happy about it. It's like saying, That particular girl is enjoying her rice very much.

Choice of Words: The is an article that refers to a specific noun. Girl is a noun that refers to a young female child. Happily is an adverb that means with joy or pleasure. Ate is a verb that means to consume food. Rice is a noun that refers to a type of grain that is often cooked and eaten. When you put them together, "The girl happily ate rice" is a sentence that describes a specific young female child who is eating rice and experiencing great pleasure or happiness while doing so.