Answer:
B). She believes he is weak and won't do what needs to be done to become king.
Explanation:
Lady Macbeth in the given passage is quite alarmed as she fears that her husband is too fragile to carry out the plan of killing the king Duncan and him becoming the king. She says ('I fear thy nature') and calls him 'too full o' th' milk of human kindness' which reflects that she feels his kindness makes him weak and may prevent him from proceeding the plan. Thus, she manipulates him to keep his kindness aside and do what she wishes him to do. She rather belittles him to get her purpose solved and hence, option B is the correct answer.