The correct answer is C. than.
The sentence “No sooner did he go in than he came out” is an example of a correlative conjunction. Correlative conjunctions are pairs of words that are used to join two equal parts of a sentence. In this case, the correlative conjunction is “no sooner…than.” The word “no sooner” indicates that the action in the first part of the sentence happened very quickly after the action in the second part.
The other options are not correct because they do not express the same meaning as “no sooner…than.” The word “then” indicates that the two actions happened in sequence, but it does not indicate that the first action happened very quickly after the second action. The word “when” indicates that the two actions happened at the same time. The word “and” indicates that the two actions happened together.
Here are some other examples of correlative conjunctions:
- either…or
- neither…nor
- both…and
- so…that
- whether…or