4. Researchers know little about octopuses because...

Решение:

Выбираем вариант, объясняющий сложность изучения осьминогов.

1. a) it is difficult to catch them.
2. b) they are not attractive to researchers.
3. c) it is hard to understand them.
4. d) octopuses do not like strangers.

Ответ: c