MCQOPTIONS
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				| 1. | 
                                    The density of the gases (present in air) decreases with increasing altitude to such an extent, that about 70% of the mass of atmospheric air is found in the lower 5 km. of the atmosphere. This lower region of atmosphere is called the | 
                            
| A. | ionosphere | 
| B. | troposphere | 
| C. | stratosphere | 
| D. | none of these | 
| Answer» C. stratosphere | |