Final answer:
Echoic memory explains Leonard's delayed response to Jenny, as it preserves auditory information for a short period, allowing for later processing and understanding of what was heard.
Step-by-step explanation:
In the scenario described, the type of sensory memory that explains Leonard's delayed response to Jenny's question is b) Echoic memory. Echoic memory is a subset of sensory memory that specifically pertains to the temporary storage of auditory information. Our brains have the ability to retain sounds for a short period, typically up to several seconds after the sound is heard, which allows us to process and understand auditory information that we might not initially pay conscious attention to.