Answer:
A
Step-by-step explanation:
B is wrong because Brutus's decision is a further step to the climax, not the creation of it.
C It can be argued that his decision provides the resolution for him and his fellow-murderers, but the impact on the plot is another issue.
D Like C, it is in itself a correct description but it doesn´t contribute to the development and preparation of the plot, the moment of action (the murder) that is rising and coming nearer, also known as the climax.