The answer is A.bursts of light
It's are because the phrase economics is used as a plural term in the following sentence.
1. add ideas likewise: is an adverb that I used to add ideas
2. indicate order next: this connector helps put ideas in order, similar connectors are “first, second, finally”
3. show a consequence as a result: This sentence connector is used to show a consequence of a previous idea.
4. show time relation Eventually: it means at the end, as a final result
5. repetition of an idea in summary: means repeating the same idea with other words in order to summarize concepts.
6. introduce an illustration for example: this connector introduces an example or explanation of a previous idea.
7. take away, limit, or oppose yet: this sentence connector is used to introduce an opposing view or idea
8. show space relation on the left: this phrase provides a space relation
