| A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this. |
| 1. The area was sprayed with DDT by an aircraft. |
| 2. Lots of urea and phosphate fertilisers were used in the crops in the vicinity. |
| 3. Phytoplankton population in the lake declined initially .thereby greatly reducing photosynthesis |
| 4. The lake water turned green and stinky. |
| Which two of the above were the main causes offish mortality in the lake? |
A) 2 and 3
B) 3 and 4
C) 1 and 3
D) 1 and 2
Correct Answer: D
Solution :
[d] A lake near a village suffered heavy mortality of fishes within a few days because lots of urea and phosphate fertilisers were used in the crops in the vicinity and the area was sprayed with DDT by an aircraft. The other two reasons are biological in nature and that does not cause heavy mortality in short duration,
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