Which two red grape varieties are most prominent in Bordeaux?

Bordeaux is renowned for its exceptional red wines, and the two most prominent grape varieties used in the region are Merlot and Cabernet Sauvignon. Merlot is known for its softer, fruitier character and often contributes to a wine's approachability and roundness. It thrives in the clay soils found in many parts of Bordeaux, which help produce robust wines with flavors of plum, black cherry, and chocolate.

Cabernet Sauvignon, on the other hand, provides a structural backbone for many Bordeaux blends. This grape is known for its higher tannin levels, intense black fruit flavors, and potential for aging due to its acidity and robustness. The combination of these two varieties allows for a balance of fruitiness from Merlot and the depth and complexity from Cabernet Sauvignon, creating some of the world's most celebrated wines.

The other choices do not reflect the key grape varieties traditionally associated with Bordeaux, as they pertain to different regions or styles of wine.