Correct answer is (c) Twin-wire formers
For explanation: Twin-wire formers are particularly used for lightweight sheets, corrugated media and linerboard grades. In this, the paper web is formed between two converging forming screens by means of a flow box and the water is drained from the slurry by pressure and later by vacuum. A typical twin-wire forming unit is the inverform, which was designed to provide a new method for the manufacture of single and multi-ply sheets at high speeds. Successive layers of fiber are laid down sequentially on the felt, with water being removed upwardly, overcoming the difficulty experienced in the conventional downward removal of water through several layers of board at high speed.