D. The natural barrier of the Himalayas prevented the religion’s spread.
Explanation:
Water and mountains surrounded ancient India. This geographic isolation protected the people who settled in this region. It was extremely difficult for outside invaders to reach the subcontinent without making dangerous journeys over the mountains or across the ocean. Natural barriers, such as mountains, deserts, rivers, and seas, made travel to and from China challenging. The Himalayas in the west and the Gobi in the north were two important geographic barriers. They made the spread of ideas and goods between the ancient Chinese and others outside the region difficult.
So the correct answer would be:
D. The natural barrier of the Himalayas prevented the religion’s spread.
