A、Lack of oxygen. B、Overgrowth of water plants. C、Low water level. D、Serious pollution upstream. A

There are some serious problems in the Biramichi River. The local chamber of commerce, which represents the industry in the area, hired me as a consultant to do a one year study on fishing in the Biramichi River and write a report for them. This is my report:
    One of the major problems in the Biramichi River is that the level of oxygen in the water is too low. Several chemicals have displaced the oxygen. This chemical pollution has two sources: the factories which dump polluted water directly into the river and the local community which dumps untreated human wastes into the river. The local town government has already spent 2 million dollars on waste water treatment projects, but it will cost another 27 million to complete the projects. It will take at least 15 years for the town to collect enough revenue from taxes to complete these projects. The factories here employ 17,000 people in an area where there is very little alternative employment. It is not economically practical to close or relocate the factories. Also the factories cannot afford to finance chemical treatment plants by themselves. Another problem is that the members of the Biramichi fishing cooperative are overfishing. Fishes are caught when they are on the way upstream to lay eggs. Consequently, not enough fish are left to reproduce in large number. The members of cooperative say that they had already reduced their annual catch by 50 percent. However, my studies indicate that they took fewer fish because there were fewer fish to catch, not because they were trying to preserve fishes.
Q. 15. What was the speaker assigned to do in the past year?
Q. 16.What is one of the problems in the Biramichi River?
Q. 17.What does the passage tell us about the factories along the river?
Q. 18.Why was the annual catch of fish in the Biramichi River reduced according to the speaker?