Final answer:
Contrastive sounds in a language are those that can change the meaning of a word when one is substituted for another, such as /p/ and /b/ in English changing 'pat' to 'bat'.
Step-by-step explanation:
When two sounds are considered contrastive in a language, it means that c) they can change meaning in a given language. This aspect of phonology is crucial for differentiating words in spoken language.
For example, in English, the sounds /p/ and /b/ are contrastive as they can change meaning, demonstrated by the minimal pair 'pat' and 'bat', where the substitution of one sound for the other results in a different word with a different meaning.