Final answer:
Developing a multi-year strategic plan for organizational growth is most likely to be completed by a long-term group, as it requires sustained effort and coordination over a long period, in line with long-term group objectives. Therefore, the correct option is C.
Step-by-step explanation:
The task most likely to be completed by a group that has been formed for long-term assignments is developing a multi-year strategic plan for organizational growth. This kind of task requires extensive research, planning, and continuous development over an extended period. Such strategic planning often involves setting long-term goals, identifying necessary resources, considering market trends, and developing a sustainable competitive advantage, which aligns with the scope of a long-term group's objectives. In contrast, tasks like shortlisting vendors for a one-time event, conducting quick market analysis, or creating a budget for a short-term marketing campaign are typically shorter in duration and might be undertaken by groups or individuals that focus on short-term or ad-hoc projects.
Collective behavior is exemplified by activities where a group of people act together.