A.) feasible
Feasible is the only word that makes sense in this sentence. A synonym for feasible is possible. The speaker says that the goals are admirable meaning that they are something to be admired and respected. However, the speaker then drops the "but" which indicates that there is a change. This means that even though the goals are good, something is not right about them. The word feasible/possible is perfect because it says that the speaker doesn't think they're feasible/possible.
Magnitude is something that is big and large. Fallacious is something that is false. The goals are not false goals, just not likely to be attained. Someone who is persuasive can easily convince someone of something.