JEE Math Practice Question

A variable plane passes through a fixed point (3,2,1) and meets x, y and z axes at A, B and C respectively. A plane is drawn parallel to yz -plane through A, a second plane is drawn parallel zx-plane through B and a third plane is drawn parallel to xy-plane through C. Then the locus of the point of intersection of these three planes, is :

1. A.$${x \over 3} + {y \over 2} + {z \over 1} = 1$$
2. B.x + y + z = 6
3. C.$${1 \over x} + {1 \over y} + {1 \over z} = {{11} \over 6}$$
4. D.$${3 \over x} + {2 \over y} + {1 \over z} = 1$$