The train had already gone ___ I reached the station.

Correct option is B

“When” correctly connects two actions that happened in sequence. Explanation of options: • (a) ✘ “Whenever” suggests repetition, not one-time event. • (b) ✔ “When” indicates the timing of reaching the station. • (c) ✘ “But” shows contrast, not used with time clauses. • (d) ✘ “Because” implies reason, not appropriate here.