Read the passage carefully.

To the south and southeast of China are the Himalaya Mountains. These are the highest mountains in the world. They provided a nearly impassable border for Ancient China, keeping the area isolated from many other civilizations. They were also important to Chinese religion and were considered sacred.

– “Ancient China: Geography,”

Ken Nelson

Using context clues, which phrase best defines the word impassable?

separate or apart
tall and forbidding
unable to be crossed
of divine or holy origin