Final answer:
The wall frescoes in the House of the Vettii predominantly featured the visual effect of trompe-l'oeil, creating an illusion of three-dimensional space. The correct answer is option A).
Step-by-step explanation:
The artists who created the wall frescoes in the House of the Vettii incorporated the visual effect of trompe-l'oeil. This technique is used to create an optical illusion that objects exist in three dimensions. Other ancient and Renaissance painting techniques included Sfumato and Chiaroscuro, which were used to create subtle transitions and a play of light and shadow, respectively, although they are not specifically attributed to the House of the Vettii. Pointillism was a technique developed much later, in the 19th century, and is therefore not relevant to the frescoes in question.