The key word for "third" is 'sequence' because it develops an idea related to events which occurred before and the author uses this adverb to continue sequencing a story, an anecdote or an event.
This adverb is usually used in story-telling and helps the author/speaker indicate what happened before and what happened after.
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Examples of key words for the other options:
- adding an idea: and, furthermore, in addition, etc.
- explanation or illustration: for example, in other words, to illustrate, etc.
- emphasis and purpose - time: indeed, previously, above all, etc.
-repetition and summary: again, to sum up, in sum, etc.