1. The common house sparrow once seen everywhere in large numbers in Mumbai has become scare in many areas, and this is causing concerns not only to bird lovers but also to scientist.
A. The declining bird population could mean that air pollution levels in the metropolis are rising dangerously; or, since sparrows are grain eaters, it could indicate that the people are consuming certain higher dosages of pesticides than before.
B. Today, if sparrows of Mumbai are in distress it could be a warning to human resident.
C. Formerly, miners used to carry canaries down into the mines with them.
D. If the canaries showed signs of distress it indicate that there were poisonous gases in the air, and the miners would immediately leave the mine.
6. In some countries like Britain, the quality of the environment is graded according to the number of bird species found in the locality.
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