The correct answer is option 1: Fibrous plants.

In the paper manufacturing industry, fibrous plants are essential because they provide the necessary raw material for the production of paper. The fibrous plants used for paper production have long and strong fibers that can be converted into pulp. These fibers provide the necessary strength and flexibility to the paper.

Option 2, Orchids, are not commonly used in the paper manufacturing industry. Orchids are known for their beauty and are primarily used for ornamental purposes.

Option 3, Non-flowering plants, may not be suitable for paper production as they do not have strong fibers required for papermaking.

Option 4, Plants growing in high altitude, is not necessarily relevant to the paper manufacturing industry. The altitude at which a plant grows does not determine its usefulness in paper production.

Therefore, option 1, Fibrous plants, is the correct answer as they are an essential raw material in the paper manufacturing industry.