The periodic change in temperature in the Pacific Ocean is known as .............

Domestic waste will result in ..........

$A$ lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this.
$A.$ Lots of urea and phosphate fertilizer were used in the crops in the vicinity.
$B.$ The area was sprayed with $DDT$ by an aircraft.
$C.$ The lake water turned green and stinky.
$D.$ Phytoplankton populations in the lake declined initially thereby greatly reducing photosynthesis.
Which two of the above were the main causes of fish mortality in the lake?

Which of the following steps can be taken to control global warming?
$I-$ Reducing the use of fossil fuels.
$II-$ Improving energy efficiency.
$III-$ Deforestation.
$IV-$ Afforestation.
$V-$ Increasing human population growth.

Which one of the following statements is $NOT$ correct?

$A$ large number of fish suddenly die in a lake near a village. Which of the following could be the reason for this?
$(a)$ Excessive use of urea and phosphate fertilizers in nearby fields.
$(b)$ Spraying of $DDT$ in the entire area.
$(c)$ The lake water has turned green and murky.
$(d)$ The population of phytoplankton in the lake has decreased,reducing the photosynthetic capacity.
Which two of the above reasons are responsible?