The correct statement regarding focus groups is:
Researchers should closely monitor the discussion to prevent individuals dominating responses.
This is true because it's important for facilitators to ensure that all participants have the opportunity to share their views and that the discussion remains balanced.
The other statements are not accurate in the context of focus groups. Participants do not have to be chosen at random, focus groups are qualitative in nature and therefore do not provide data similar to a checklist, and they can still be useful even when time is limited, although the depth of discussion may be affected.