The weakest sound that can be heard by a person in a quiet environment is equivalent to ____________ decibel ?

A. Air
B. Water
C. Noise
D. Radioactive

A. Ionosphere
B. Troposphere
C. Stratosphere
D. None of these

A. Hydrochloric acid
B. Lime
C. Copper sulphate
D. Sodium sulphate

A. Use of silencers
B. Green house gases
C. Vibration damg
D. Tree plantation

A. Volcanic eruptions and lightening discharges
B. Biological decay of vegetable matter
C. Photochemical oxidation of organic matter
D. None of these

A. Thermal power plant
B. Petroleum refinery
C. Nitric acid plant
D. Sulphuric acid plant