Answer:
The answer is D.
Step-by-step explanation:
It is possible to reach this conclusion by process of elimination.
A is NOT the answer because the paragraph implies the opossite: that you need a higher concentration after a task has become too repetitive.
B is NOT the answer because the text clearly states that the brain activity occurs before and not after the mistakes are made.
C is NOT the answer because, firstly, it was the same research and not "another". And secondly, the paragraph never says that region X is directly associated with repetitive tasks, only that is active shortly before mistakes are made.
E is NOT the answer because the next never mentions any relation to sleep related regions of the brain.
Thus D is the only right answer, and it's actually a very good summary of the paragraph.