Final answer:
The sentence 'The boy was running and then he fell.' should be segmented into two C-units because it contains two main clauses that can function as complete sentences independently.
Step-by-step explanation:
The question is asking which sentence, among the given options, should be divided into two C-units. A C-unit, in linguistics, often refers to a clause or a single independent sentence which conveys a complete thought. In evaluating the given sentences, we should look for one that consists of two distinct clauses that can function independently.
Option 2: 'The boy was running and then he fell.' is the sentence that should be segmented into two C-units. This sentence contains two main clauses, 'The boy was running' and 'then he fell', which can each stand alone as a complete sentence. Options 1, 3, and 4 do not require segmentation into two C-units as they are either simple sentences with a single clause or a complex sentence with a dependent clause that cannot stand alone.