[?] pollution causes [?] diseases such as asthma and bronchitis.
[?] can be used to indicate the level of air pollution. In areas of low
pollution there are [?] types of lichens and they are present in [?] numbers.
Water pollution decreases [?] levels in the water. Decreased [?] levels
in water will kill some water [?] and animals. Freshwater invertebrates can be used
to show the level of [?] pollution. In areas of [?] pollution there are more types of
[?] and in greater numbers.
[?] pollution prevents plants from growing properly and gradually poisons [?].