I think it is D.) Scientist have spent years trying to determine how tsunamis can be predicted with greater accuracy.
Explanation:
Words like ain't, you guys, or y'all would not be worlds you would want to put in a formal style or tone.
So, words such as determine, predicted, and greater accuracy, are formal in a way. Just think of it this way, the sentence would sound as if someone who was smart was speaking or someone who is very FORMAL.
