The transition word in the passage you provided is "and." However, since "and" is not one of the options listed in your question, I cannot identify a transition word from the available choices (next, when, across, over).
If the goal is to find a word that indicates the sequence of events, "when" could serve as a transition word, as it introduces a time relationship.
If you have the option to choose "when," that would be the best choice based on the context provided.