Which of the following is a major DECA conference?

The International Career Development Conference (ICDC) is a major DECA conference because it serves as the pinnacle event for DECA members, showcasing their skills and achievements in various business-related areas. This conference provides an opportunity for high school and college students to participate in competitions, attend workshops, and network with industry professionals and fellow DECA members from around the world. It plays a critical role in DECA's mission to prepare emerging leaders and entrepreneurs by allowing participants to demonstrate their knowledge and skills in real-world settings.

The other options, while they may sound plausible or related to business and professional development, are not official major conferences organized by DECA. The National Sales Conference and the Global Marketing Symposium do not hold the same significance or recognition within the DECA community as the ICDC, while the International Business Summit, though it may focus on relevant topics, is not a primary conference hosted by DECA. Thus, ICDC stands out as the correct answer due to its importance and wide-reaching impact on DECA members' experiences.