Final answer:
The relative clause in the sentence is 'that are not registered,' which provides additional details about the subject 'cars.' Relative clauses help to specify and give context to nouns within sentences.
Step-by-step explanation:
The sentence provided contains a relative clause, which is a type of dependent clause that modifies a noun or pronoun. In the sentence 'All cars that are not registered will be towed to the nearest impound lot,' the relative clause is 'that are not registered.' This clause modifies the noun 'cars' by providing additional information about which cars will be towed.
In grammar, the use of relative clauses is to provide extra details about the subject of the sentence. For example, in the sentence 'Her truck, a red Chevy, was parked around the back of the house.' the phrase 'a red Chevy' is a noun phrase used adjectivally to describe 'truck.'
Relative clauses can greatly enrich sentences by offering specificity, as seen with the colon being used in the sentence 'Road construction may affect morning commute times: the collision on the highway has closed two lanes.' Here, the colon introduces additional detail that completes the idea presented in the first part of the sentence.