The deep ocean is as challenging to explore as __________ space; we have more detailed maps of the surface of Mars than the ocean floor

Прочитайте текст с пропуском. В ответе запишите цифру 1, 2, 3 или 4, соответствующую выбранному Вами варианту ответа.

The deep ocean is as challenging to explore as __________ space; we have more detailed maps of the surface of Mars than the ocean floor.

1. isolated
2. deep
3. distant
4. long