The first one is the correct answer..no commas needed
The writer is trying to inform the audience.
Answer:
The river water can also be used for irrigation purposes. Agriculture is the main occupation of Nepali people, so irrigation is of great significance.
Answer:
A prepositional phrase is a modifying phrase which includes a preposition (in this case, "over") and the object of the preposition (in this case, "the mantelpiece.")
