Passage Summary: Since gravity is what makes tides happen, the author assumes gravity is the only reason why some places have much bigger tides than others.

Conclusion: The specific size of tidal ranges is determined solely by the gravitational pull of the sun and moon.

Reasoning: Gravity from the sun and moon are the only forces that actually create the tides.

Analysis: The author commits a classic error by assuming that the primary cause of a phenomenon is the only factor that determines its local intensity. While gravity 'induces' the tides, it doesn't necessarily follow that gravity alone explains why the Bay of Fundy has a seventeen-meter range while other places do not. The argument ignores local variables like coastal shape or underwater geography that might amplify the effect. Look for an answer that identifies this failure to distinguish between the source of a force and the factors that influence its local magnitude.