The given reaction sequence involves the desulfonylation of a sulfonium salt followed by hydrogenation using a Raney-Nickel catalyst. Let's break down the process:

Sulfonium Salt Formation: The starting compound is a sulfonium salt. In the reaction, the presence of the sulfonium group is crucial as it acts as a leaving group. Here, the leaving group potential is realized under basic conditions.

Use of KO^tBu (Potassium tert-butoxide): KO^tBu acts as a strong base. It is used to deprotonate and generate a carbanion by removing the sulfonium group, leading to a bicyclic compound with an olefin (double bond) formation.

Raney Ni Catalysis: Raney nickel is a special type of nickel used for catalytic hydrogenation. When heated (Δ), it facilitates the hydrogenation of the olefin formed in the previous step. This results in the saturation of the double bond.

The major product formed after these two steps is the saturated bicyclic compound is

Thus, the correct answer is the structure that depicts the saturated bicyclic compound formed from the original sulfonium salt after the reaction sequence.