Many linguists contend that language acquisition in children is not merely an imitative process but rather an innate capacity that allows them to ______ complex grammatical rules from exposure to speech, even when the input is imperfect.

✓ Correct Answer: Option C

The sentence suggests children use an innate capacity to '______ complex grammatical rules' from exposure. 'Derive' (obtain something from; deduce or infer) best fits the idea of extracting or learning rules from observed speech patterns.