Final answer:
Using the given clues about seating arrangement, it is deduced that Clyde is seated immediately to the left of Felix.
Step-by-step explanation:
The puzzles requires determining the seating arrangement of six friends at a rectangular table based on the given clues. According to the clues, Adam and Dorky are seated at the ends of one side without anyone to their right, which means they are at the far right from their own perspectives. Similarly, Clyde and Benjamin are on the ends of the opposite side without anyone to their left, placing them at the far left from their own perspectives. Adam and Benjamin cannot be on the same side, so if Adam is on the right end of one side, Benjamin must be on the left end of the opposite side. Since Ethan cannot sit next to Dorky and Adam's right side is empty, Ethan must sit to the left of Adam. Now, Dorky must be at the right end of the opposite side, and since Benjamin is on the left of that side, Felix must be between Dorky and Benjamin. Now the only person left to fill the seats is Clyde, who must be to the left of Felix. Therefore, the answer is D. Clyde is seated immediately to the left of Felix.