Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R). In the light of the above statements, choose the most appropriate answer from the options given below:

Organic pollution in rivers becomes most severe during the hot summer months, so the Assertion is correct.

Warm conditions intensify the depletion of dissolved oxygen in the water.

The Reason is correct and directly explains it, because higher water temperature both lowers oxygen solubility and speeds up microbial decay.

Warmer water holds less dissolved oxygen while decomposers work faster and demand more of it.

The combined effect leaves rivers with dangerously low oxygen just when pollution loads are high.

This is why fish kills are more common in polluted rivers during summer.