In the arrangement shown in figure the ends P and Q of an unstretchable string move downwards with uniform speed U. Pulleys A and B are fixed. Mass M moves upwards with a speed [IIT 1982]

• A.             \[2U\cos \theta \]                   
• B.             \[U\cos \theta \]            
• C.             \[\frac{2U}{\cos \theta }\]                  
• D.             \[\frac{U}{\cos \theta }\]