Read the passage carefully and choose the best answer to each question out of the four alternatives. Manja, or the glass-coated string used for flying kites, not only poses threat to humans, animals and birds but also to trees. A study by the country's oldest botanical garden has revealed that it poses a great threat to trees. But how can a snapped string struck in a tree kill the tree? Apparently, it does so by allying with the creepers in the garden. A research paper by three scientists of the Acharya Jagdish Chandra Bose Indian Botanic Garden, located in West Bengal's Howrah district, illustrates in detail how the manja, in collusion with climbers, does the damage. "The abandoned, torn kite strings act as an excellent primary supporting platform for the tender climbers, giving easy passage to reach the top of the trees. Lateral branches from the top of the climber and other accessory branches from the ground reaches the top taking support of the first climber, completely covers the treetop, thus inhibiting the penetration of sunlight," says the research paper. How many scientists contributed to a study by country's oldest botanical gardens on how manja can kill a tree?