In Research Reported by Richard Hackman, Which of the Following

In research reported by Richard Hackman, which of the following was found concerning the use of a planning session in working groups?

A) Planning was not generally useful.
B) Planning was always useful.
C) Planning was useful, but only if the groups were diverse.
D) Planning was useful for tasks in which information had to be shared among group members, but was not useful on tasks in which information did not need to be shared.