Please explain why A isn't a necessary assumption

@amf, Let's look at (A). (A) says, "Larson has the assertiveness the task requires." (A)'s negation would say, "Larson DOES NOT have the assertiveness the task requires." We know from the stimulus that Larson can't do the task because of a scheduling conflict. We do not know anything about his assertiveness, nor do we care about it. Why? Well, it does not matter if Larson could do the task otherwise because we already know that the can't do it. Thus, the only necessary premises to arrive at the conclusion that Parker must do it are that Larson can't do it, Franks can't do it, and no one else can do it. Thus, (A)'s negation doesn't wreck the argument, so it's out. Does this make sense? Let us know if you have any other questions!