As a scrum master, how should you proceed with sending an invitation to the retrospective meeting

a$.$ The team tends to discuss and complain very much so he should set the meeting for $4$ hours.

b$.$ He should invite for a $2$ hour session and moderate the session.

c$.$ He should invite the session in front of the sprint board, this way the team could directly talk about the tasks and results of the sprint.

d$.$ He should reserve a separate room. This will create an environment that will allow open discussions.

e$.$ Besides the scrum team, the PO should also be invited to the meeting.

f$.$ The PO should not be invited as the team will not speak honestly about their problems if he is there.

$=AF$

$=$BDE

$=$ACE