\[ABC\] is a right angled triangle in which \[AB=3\,cm\] and \[BC=4\,cm\]. And Ð ABC = p/2. The three charges \[+15,\ +12\] and \[-20\,e.s.u.\] are placed respectively on \[A\], \[B\] and \[C\]. The force acting on \[B\] is

• A.          \[125\ dynes\]      
• B.          \[35\ dynes\]           
• C.          \[25\ dynes\]    
• D.          Zero