Topic: Sequence of Tense,

Best Answer Explained in Below-:

The sentence "No sooner had Kashem left, Karim came" employs a specific construction that indicates a cause-and-effect relationship between two actions, with an emphasis on the immediacy of the second action following the first. The phrase "No sooner...than" is a common English idiomatic expression used to show that one event occurs almost instantaneously after another.

In this context, the word "than" effectively signals the rapid succession of events: as soon as Kashem departs, Karim arrives. This construction emphasizes the quickness and direct link between the two actions. The other options (B: then, C: when, D: after) do not convey the same immediacy or causal connection. "Then" suggests a sequential order that might not emphasize the immediacy, while "when" could imply a more general occurrence without the same urgency. Lastly, "after" suggests a broader gap in time between events, which conflicts with the intent of the original sentence.

Thus, "than" is the appropriate choice, as it reinforces the notion that Karim’s arrival follows immediately upon Kashem’s departure.