Which of the following wines must contain a minimum of 70% Sangiovese for its classification?

The classification of Vino Nobile di Montepulciano requires that the wine contains a minimum of 70% Sangiovese, specifically the local clone known as Prugnolo Gentile. This high percentage of Sangiovese is integral to the wine's identity, contributing to its characteristic flavors, structure, and aging potential. Vino Nobile di Montepulciano is a renowned Tuscan wine, celebrated for its complexity and the influence of the region's terroir.

In contrast, the other wines listed have different grape composition requirements. Barbaresco, for example, is primarily made from Nebbiolo, while Montepulciano di Abruzzo is predominantly made from the Montepulciano grape, and Chianti Classico, while it also includes Sangiovese, has varying percentage requirements depending on the specific regulations but does not necessitate as high a percentage as 70%. Thus, the requirement for Vino Nobile di Montepulciano to have at least 70% Sangiovese is what distinguishes it from the other options.