The answer to this sort of test questions depends a lot on the context that the supporting study material has introduced. In a real work setting, both answers could be correct, or even both be wrong.
As David Espina mentions in the other answer, the proper action taken by the project manager depends on a lot of variables that are absent in the question (thus, the context that the study material has put forth should fill in the assumptions).
Based on the way the question is worded, and from B being the selected answer, it seems to be asked in an Agile context of some sort, and Agile relies a lot on self-organizing and self-managing teams. The team figures out how to handle things by inspecting and adapting.
Answer B implies giving the team room to figure it out on their own. Answer A seems to imply toward a more traditional command and control approach.
So that's my assumption for selecting B as the answer. Is that supported by the material of the course?