The girl laughs happily.
Meaning: This sentence describes a girl who is laughing and appears to be happy. It could be a child laughing with her friends or a young woman enjoying a funny joke.
Choice of Words: Girl refers to a female child or a young woman. Laughs is an action done by the girl, which is laughing. Happily describes the emotional state of the girl, which is happy.
Alternative Expressions
Related Expressions