Which of the following is NOT one of the top three white grape varieties in Argentina?

Riesling is not among the top three white grape varieties in Argentina. The country's white wine production is dominated by Torrontés, which is known for its aromatic profile and is often considered the flagship white variety of Argentina. Chardonnay is also prominent, appreciated for its versatility and ability to produce high-quality wines, both in oaked and unoaked styles. Viognier, while gaining some attention, does not compete with the widespread popularity and production levels of Torrontés and Chardonnay. Thus, listing Riesling, which is not widely cultivated in Argentina compared to these other varieties, as the correct answer reflects an understanding of Argentina's top white wine grapes.