Question 151·Medium·Rhetorical Synthesis
While preparing a presentation on rechargeable batteries, a student has compiled the following notes:
- Lead-acid batteries, invented in 1859, are heavy and have low energy density; they are still used to start car engines.
- Nickel–metal hydride (NiMH) batteries are lighter than lead-acid batteries and offer moderate energy density, but they can lose charge quickly when not in use.
- Lithium-ion batteries, introduced in 1991, provide the highest energy density of the three types and are the lightest; they also suffer little from the memory effect.
- Lithium-ion batteries are generally more expensive than both lead-acid and NiMH batteries.
The student wants to highlight how lithium-ion batteries differ from lead-acid and NiMH batteries specifically in terms of energy density and weight. Which choice most effectively uses relevant information from the notes to achieve this aim?
For rhetorical synthesis questions based on notes, underline exactly what the question says the writer wants to emphasize (for example, a specific comparison, cause-and-effect, or trend). Then scan the notes and keep only the information that matches that focus. Eliminate choices that introduce off-topic details, and pick the option that most directly and completely uses the relevant notes without adding unrelated points.
Hints
Focus on what the question asks you to emphasize
Underline the words in the question that state what the student wants to highlight—what are the two specific characteristics being compared?
Filter the notes for only those characteristics
In the notes, find the phrases that talk about those two characteristics for each battery type. Ignore information about history, applications, cost, or memory effect.
Eliminate choices that drift away from the target
Cross out any answer choices that mainly discuss when the batteries were invented, what they are used in, how much they cost, or how they handle the memory effect.
Check for a complete three-way comparison
Among the remaining options, choose the one that mentions all three battery types and compares them along the two characteristics you identified.
Step-by-step Explanation
Clarify the task in the question
The question says the student wants to highlight how lithium-ion batteries differ from lead-acid and NiMH batteries specifically in terms of energy density and weight.
So the correct sentence must:
- Talk about all three battery types (lead-acid, NiMH, and lithium-ion), and
- Compare them only on energy density and weight (how heavy/light they are and how much energy they store).
Identify relevant notes
From the notes, keep only the parts about weight and energy density:
- Lead-acid: heavy; low energy density
- NiMH: lighter than lead-acid; moderate energy density
- Lithium-ion: lightest; highest energy density
Ignore history, applications, memory effect, and cost because they are not the focus of the question.
Evaluate the choices for that exact comparison
Eliminate any choice that emphasizes applications, cost, memory effect, or history instead of comparing weight and energy density across the three battery types.
The correct choice must include all three types and clearly contrast them using only those two characteristics.
Select the choice that matches the aim
The only option that compares lead-acid, NiMH, and lithium-ion batteries on both weight and energy density is:
“Lead-acid batteries are heavy and low in energy density, NiMH batteries are lighter with moderate energy density, but lithium-ion batteries are the lightest and offer the highest energy density.”