Final answer:
The lines from Macbeth signify his acknowledgment of being so deeply involved in his crimes that there is no turning back, which is why option A is the best fit.
Step-by-step explanation:
The lines "By the worst means the worst. For mine own good, All causes shall give way. I am in blood Stepped in so far, that should I wade no more Returning were as tedious as go'er." are significant because they reveal Macbeth's realization that he has committed irreversible acts. The choice that fits best with the meaning of these lines is A. Macbeth reflects on the consequences of his actions and realizes there is no turning back. In this speech, Macbeth acknowledges that he has delved too deep into his crimes to retreat, suggesting that continuing on his violent path is as difficult as to return to his former, innocent self. Therefore, the lines signify a point of no return for Macbeth where he contemplates that for his own benefit, he has to push aside all moral and ethical concerns ('All causes shall give way'). He also acknowledges that he is so steeped in bloodshed that going forward is as arduous as trying to go back to his previous life.