Correct answer: (b) 2 and 3 only
Explanation
- A
1 only
(a) 1 only. Heavy sand mining does not characteristically decrease river salinity; in coastal reaches it can worsen saline intrusion. Statement 1 is therefore not a valid consequence. This option is not the key.
- B
2 and 3 only
(b) 2 and 3 only. Removing the sand aquifer’s filter and storage lowers the water-table and can pollute groundwater by exposing it to river contaminants and by damaging the hyporheic buffer. Statements 2 and 3 follow; 1 does not. This option is the official key.
- C
1 and 3 only
(c) 1 and 3 only. Water-table fall (3) is real, but decreased salinity (1) is not the expected effect. This option is not the key.
- D
1, 2 and 3
(d) 1, 2 and 3. Statement 1 is wrong, so the full set fails. This option is not the key.
Summary. Official key is (b) 2 and 3 only. River-bed sand stores and filters water. Mining it lowers the local water-table and can contaminate groundwater. Salinity in the channel is not thereby decreased; coastal mining may even pull the salt wedge inland. Statement 1 therefore drops. The surviving consequences are pollution of groundwater and lowering of the water-table.
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