Final answer:
The correct option that combines the two sentences using a coordinating conjunction is A. The scientists could see the data in front of them, yet there were some who still wouldn't believe.
Step-by-step explanation:
The correct option that combines the two sentences using a coordinating conjunction is:
A. The scientists could see the data in front of them, yet there were some who still wouldn't believe.
The coordinating conjunction 'yet' is used to show a contrast between the two independent clauses. It indicates that despite the scientists being able to see the data, there were still some who refused to believe.