Answer:
The sentence has a dangling modifier.
Explanation:
A Dangling modifier is a complete phrase or clause that doesn't logically fit the rest of the sentence and it modifies the incorrect word. "They spotted a pod of killer whales driving along the ocean highway" gives the idea that the killer whiles were driving, therefore "driving along the ocean highway" is the dangling modifier and the correct sentence should be "Driving along the ocean highway, they spotted a pod of killer whales."
