 
			 
			MCQOPTIONS
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				| 1. | The single stack system if effective only in the case when the traps are filled with water seal of depth not less than _________ | 
| A. | 15 mm | 
| B. | 50 mm | 
| C. | 75 mm | 
| D. | 100 mm | 
| Answer» D. 100 mm | |