Final answer:
Option 'b. how hurricanes originate.' is a complete sentence as it contains both a subject and a verb and expresses a complete thought.
Step-by-step explanation:
The question asks which of the following groups of words is a complete sentence:
- a. we now know
- b. how hurricanes originate.
- c. how they affect ecology.
- d. both of the above.
- e. neither of the above.
A complete sentence must have at least a subject and a verb, expressing a complete thought. Based on the options provided, 'b. how hurricanes originate.' is a complete sentence because it has a subject ('how hurricanes') and a verb ('originate'). The other options are either fragments or incomplete thoughts, and thus do not constitute a complete sentence.