According to the French traveller Tavemier, the majority of houses in Varanasi during the 17th century were made of brick and stone. This means that the buildings were constructed using a combination of these two materials.

Option 1 suggests that the houses were made of brick and mud. However, this contradicts the information provided by Tavemier, who specifically mentioned the use of stone instead of mud.

Option 2 suggests that the houses were made of stone and thatch. Again, this contradicts the information provided by Tavemier, who did not mention the use of thatch as a building material.

Option 3 suggests that the houses were made of wood and stone. While this may have been the case for some houses, it is not the majority as stated by Tavemier.

Therefore, the correct answer is option 4, which states that the houses were made of brick and stone. This aligns with the information provided by Tavemier and best represents the majority of houses in Varanasi during the 17th century.