Answer:
The correct answer seems to be letter D. They imply that scientists have studied squid that washed up.
Step-by-step explanation:
The question does not concern the whole text, but only the lines:
"We also know they feed on deep-sea fish and other squid. We know this because of all the giant squid that have washed ashore."
That's why the correct answer is letter D. According to these lines, what we know about giant squids was what scientists were able to study by using squids that were washed up or washed ashore. No one has ever caught a giant squid, which makes them quite rare to study. The ones that do wash ashore are usually already dead, or at the verge of dying, since the atmospheric pressure up here is too low for them to stay alive for long.