With his sub-four minute mile Bannister broke a psychological barrier

The issue here is the sequence of events; whether Bannister inspired after breaking the barrier or he inspired as he broke the barrier simultaneously. As you may see, simultaneously does not make sense here. We have to take that the breaking and inspiring are two separate events and that inspiring followed breaking. Hence the need for the conjunction ‘and’

Inspiring does not just modify the barrier alone as has been remarked. It points to the entire idea that includes the breaking of the barrier; the modification is ok in B. But still B is not the answer because it expresses the sequence of breaking and inspiring simultaneously. D is the best answer