The correct answer is A. Beas.
Manali is a town in the Indian state of Himachal Pradesh. It is situated in the Kullu Valley, on the banks of the Beas River. The town is a popular tourist destination, known for its scenic beauty, temples, and monasteries.
The Beas River is a tributary of the Indus River. It is the longest river in Himachal Pradesh, and the fifth longest river in India. The river originates in the Beas Kund, a glacial lake in the Pir Panjal Range. It flows through the Kullu Valley, and then through the Kangra Valley before joining the Indus River near Tandi.
The Sultej River is a tributary of the Beas River. It originates in the Pir Panjal Range, and flows through the Kullu Valley before joining the Beas River near Manali.
The Spiti River is a tributary of the Chenab River. It originates in the Spiti Valley, and flows through the Lahaul and Spiti district of Himachal Pradesh before joining the Chenab River near Tandi.
The Chenab River is a tributary of the Indus River. It originates in the Zanskar Range, and flows through the Ladakh region of Jammu and Kashmir before joining the Indus River near Leh.