Answer:
b.The group may be dominated by a single person.
Explanation:
As for the given instance, it is clear that Harriet did not speak much in the conversation and that is why she might not have been able to disclose properly all her intentions and opinions towards the concerned topic.
Although Simon have stated all his opinions, that does not mean all his suggestions are right and he shall work upon them.
But still his opinions were that might be included most in the final decisions.
Thus, the drawback that can be clearly highlighted is that:
The group does consider only the person who is able to communicate maximum, and therefore statement B is most accurate to define the drawback.