Environmental pollution can be controlled by
A. spraying insecticides and pesticides.
B. the open burning of tree stumps.
C. treating factory wastes before disposing them.
D. disposing hot water from the power station into the sea.

Hint: We know that any undesirable change in the environment is defined as environmental pollution. Among the options given in this problem, three out of four cause environmental pollution whereas only one can control it. Therefore, we will discuss each option individually and then reach our final answer.

Complete answer:
Option A: We know that insecticides and pesticides contain chemicals. These chemicals can harm the land by reducing its fertility. Thus, spraying insecticides and pesticides can cause environmental pollution rather than controlling it.

Option B: The open burning of tree stump produces smoke which contains harmful gas such as carbon monoxide. This can pollute the air thus causing air pollution. Therefore, this also cannot control the environmental pollution.

Option C: We know that factory waste contains many harmful elements which can cause environmental pollution if it is not treated before its disposal. Thus, by treating factory wastes before disposing them can control the environmental pollution.

Option D: If the hot water is disposed directly into the sea from the power plant, it will badly affect the flora and fauna of the sea life. Thus, this will cause water pollution.From this discussion, we can say that environmental pollution can be controlled by treating factory wastes before disposing them.

Hence, option (C) is the right answer.

Note: In this question, we have seen different types of environmental pollution. This can be classified into four main types: air pollution, water pollution, land pollution and noise pollution. Any of these pollution will directly or indirectly affect life on the earth and therefore it must be controlled properly.