How can a team avoid groupthink?

Question $8$ options:

a$)$

Set up two teams with the same goal and then evaluate them.

b$)$

Certain members should be tasked with playing the devil's advocate at each step in the team's life$-$cycle.

c$)$

For each team meeting, listen to naysayers and alternative ideas first.

d$)$

Task each member to evaluate each step, providing ideas and doubts critically.