Explanation:

The Quadrilateral Security Dialogue (QSD), commonly known as the Quad, is a strategic security dialogue between four countries: **Australia, India, Japan, and the United States**. This informal strategic forum is maintained by semi-regular summits, information exchanges, and military drills between member countries. Option (A) lists New Zealand, Taiwan, and Indonesia, which are not part of the Quad. Option (B) lists Malaysia, Thailand, Indonesia, and Vietnam, which are all Southeast Asian nations but do not constitute the Quad. Option (C) lists Turkey and Brazil, which are geographically and strategically unrelated to the Quad's Indo-Pacific focus. Therefore, the correct combination of countries forming the Quad is Australia, USA, Japan, and India.