Which of the following are said to be possible reason(s) for the decline of Indus Valley civilisation as per various studies on its decline?

The correct options are
A Increasing population, which made the administration difficult.
B The course of river Indus changed and it caused floods in some areas and droughts in others
D The Aryans invaded India.
There are many possible reasons for the decline of Indus Valley civilisation as per various studies on its decline.
Some studies say that the increasing population made the administration difficult. Garbage piled up on streets, drainage systems broke down, and houses were built on roads. Too much grazing by their plentiful herds destroyed the green cover. Increasing demands of wood for fuel led to deforestation.

Other possible reasons are thus:
1) The course of river Indus changed and it caused floods in some areas and droughts in others.
2) One more popularly debated reason for the decline of Harappans is that - The Aryans invaded India.