The correct answer is "B".
President Lincoln reflects his concern with the words "I answer it only because I fear you would misconstrue my silence.", as this reflects that he is truly preoccupied with the matter, as he considers it of great importance.
On the other hand, the phrase "and they can never have a more shallow pretext for breaking up the government or extorting a compromise, than now." reflects the boldness by which President Lincoln tries to make his position clear to James T. Hale towards a potential secession.