S1. A scientific theory is first proposed as a hypothesis. S2. After it is subjected to inquiry and is proven, it becomes a thesis. The second statement:

Statement S1 describes the initial stage of scientific theory formation—as a hypothesis. Statement S2 continues the narrative by describing what happens after the hypothesis stage—namely, that following inquiry and proof, it becomes a thesis. S2 thus extends the timeline and process described in S1 by adding subsequent stages. It does not prove or challenge S1; it builds upon and continues it. Therefore, option (d) 'extends the first' is correct.