The indus, ganges, and brahmaputra were
important to ancient india because they were
(1) high mountain ranges that protected india
from invasion
(2) great rivers that flowed through india’s fertile
northern plain
(3) aryan gods to whom the priests prayed for
rain
(4) ruling dynasties that united the people of
harappa and mohenjo-daro

The correct answer is - (2) great rivers that flowed through India's fertile northern plain.

Indus, Ganges, and Brahmaputra were and still are great rivers that run through the northern fertile plains of India. These three rivers have been the basis for sustaining large populations for thousands of years and give opportunity for the development of the civilizations on the Indian subcontinent. These rivers were creating fertile plains with alluvial soil around their banks from their annual floodings, the constantly fertile renewed soil gave the people the needed basis for producing huge amounts of food and thus manage to sustain themselves and also for trade, as well as allowing the building large vibrant cities and villages. Also their waters have been used for irrigation throughout the dry period of the year. Nowadays, unfortunately, all three rivers are heavily polluted and in desperate condition.

The correct answer is 2. The Indus, Ganges, and Brahmaputra were important to ancient India because they were great rivers that flowed through India's fertile northern plain.

Explanation:

-The Indus is the most important river in Pakistan.  The river is 2880 km long and originates in western Tibet. To the north of the Himalayas, the Indus flows in a northwestern direction through Ladakh and Baltistan in India, to cross the mountains southwards with a gap. The river then flows from north to south through the fertile Indus plain in Pakistan. Here the river flows first through the Punjab region, irrigated by the five tributaries Jhelum, Chenab, Ravi, Beas and Sutlej, and then through the province of Sindh, where the green valley of the Indus contrasts strongly with the surrounding dry deserts. South of the metropolis of Hyderabad, the Indus finally reaches the Arabian Sea, into which the river with the Indus delta flows.

-Ganges is a 2,506 kilometer long river in northern India, considered one of the sacred rivers of Hinduism.  

Ganges is the holiest river of Hinduism. Its water is considered pure from sins and imparts eternal bliss. The river is therefore a target for countless pilgrimages.

-The Brahmaputra River is one of the longest rivers in Asia.  It is born in the Kubigangri glacier, near the Himalayas, and runs eastward through Chinese territory, through the western part of Tibet, passing near Lhasa. After a tour of 2896 km, it drains into the Gulf of Bengal, Bangladesh, forming part of the Ganges Delta, the largest delta in the world.