A newly developed light bulb is much more cost-effective than conventional light bulbs: it costs only about 3 times what a conventional light bulb costs but it lasts up to 10 times as long as a conventional light bulb.
Conclusion
New bulbs will sell very poorly.
Counter-evidence
New bulbs are more cost-effective than old bulbs. (costs 3 times more, but lasts 10 times as long)
Evaluate
We weren't given any reasons to think that new bulbs will sell poorly (other than their higher upfront cost), so we might see one answer saying, .
But the other answers that strengthen will just give us reasons to think that these new bulbs will sell poorly.
Goal
Eliminate four answers that make it seem like new bulbs will sell poorly. Pick the remaining answer (whether it weakens or is just irrelevant).