a. Group is a collection of 3 or more than 3 people who interact and depend on each other，and their common needs and goals make them interact with each other.
b.
- Interdependence
- Common Goal
- Group Personality
- Commitment
- Cohesiveness
- Group Conflict
- Social Facilitation
- Gender Differences
- Group Size
- Norms
c.
- Relevance
- Relatedness
- Timeliness
- Sufficient Length
- Clarity
- Informativeness
- Openness to evaluation
- Provocativeness