A) is possible, but present continous tense suggests that the 'start' is an enduring event. This is not really supportable in the context.
B) suggests a conditional - not in any way suggested by context.
C) Past simple - wrong tense to agree with the first clause.
D) Correct usage - a future event, so 'will start' is also correct, but unnecessary in common English usage,
E) Same as C)