Point charge \[q\] moves from point \[P\] to point \[S\] along the path \[PQRS\] (figure shown) in a uniform electric field \[E\] pointing coparallel to the positive direction of the \[X-\]axis. The coordinates of the points \[P,\,Q,\,R\] and \[S\] are \[(a,\,b,\,0),\ (2a,\,0,\,0),\ (a,\,-b,\,0)\] and \[(0,\,0,\,0)\] respectively. The work done by the field in the above process is given by the expression [IIT 1989]

• A.                    \[qEa\]                            
• B.            \[-qEa\]
• C.                    \[qEa\sqrt{2}\]            
• D.            \[qE\sqrt{[{{(2a)}^{2}}+{{b}^{2}}]}\]