Two converging lenses of focal lengths `f_(1)=10cm` and `f_(2)=20cm` are placed at some separation. A parallel beam of light is incident on first lens. Then,
A. for emergent beam form second lens to be parallel, the separation between the lenses has to be 30cm
B. for emergent beam from second lens to be parallel, the separation between the lenses has to be 60cm
C. if lenses are placed at such a separation that emergent beam from second lens is parallel, then the emergent beam width is 2cm if original beam has a width of 1cm
D. if lenses are placed at such a separation that emergent beam from second lens is parallel, then the emergent beam width is 4cm if original beam width is 1cm.
