KCET 2011 Physics Solved Paper

Consider the following statements in case of Young's double slit experiment.
a) A slit S is necessary if we use an ordinary extended source of light.
b) A slit S is not needed if we use an ordinary but well collimated beam of light.
c) A slit S is not needed if we use a spatially coherent source of light.
Which of the above statements are correct?