I believe the answer is a because 2 times 12 is 24. Hope this helped
        
                    
             
        
        
        
Answer:
2.25×10¯³ mm. 
Explanation:
From the question given above, we obtained the following information:
Diameter in micrometer = 2.25 μm
Diameter in millimetre (mm) =? 
Next we shall convert 2.25 μm to metre (m). This can be obtained as follow:
1 μm = 1×10¯⁶ m
Therefore,
2.25 μm = 2.25 μm / 1 μm × 1×10¯⁶ m
2.25 μm = 2.25×10¯⁶ m
Finally, we shall convert 2.25×10¯⁶ m to millimetre (mm) as follow:
1 m = 1000 mm
Therefore, 
2.25×10¯⁶ m = 2.25×10¯⁶ m /1 m × 1000 mm
2.25×10¯⁶ m = 2.25×10¯³ mm
Therefore, 2.25 μm is equivalent to 2.25×10¯³ mm. 
 
        
             
        
        
        
No, because boats and other mechanical vehicles can spill gas and oil into the freshwater. if the freshwater is scarce already, we should not contaminate it more by risking the gas and oil spills.