A problem faced by the Mekong river is that large dams in are impeding its flow and interfering migration pattern of fish and their spawning. Another problem faced is reduced water flow affecting water traffic

d. new methods of assembly are introduced.

explanation:

this allows for the goods to be made on a larger scale. not faster because now it is shown to be made better, hence the greater productivity in the question. it is calling for something new to be introduced.