Which of the following pairs are considered synonyms?

The pair "Happy/Glad" is considered a pair of synonyms because both words convey a similar meaning associated with feelings of joy and contentment. In the context of language, synonyms are words that have the same or nearly the same meaning and can often be used interchangeably in various contexts.

For instance, when someone is feeling joyful, you could describe them as happy or glad without altering the fundamental meaning of the sentence. This similarity in meaning highlights how these two words can be used in similar situations to express the same emotional state.

In contrast, the other pairs listed do not represent synonyms. "Up/Down" are antonyms, representing opposite directions; "Hot/Cold" also indicate opposite temperature extremes; "Big/Small" illustrate contrasting sizes. Recognizing synonyms helps in expanding vocabulary and understanding nuanced expression in language, while antonyms illustrate the breadth of linguistic contrasts.