16I agree with you,in all probability the answer key is wrong. Translucent objects DO form a shadow,though its intensity is nowhere near that of a shadow formed by opaque objects. Shadows are ONLY formed when light is obstructed,which cannot happen in case of transparent objects,which can happen partially in case of translucent objects,and which can fully happen in case of opaque objects. I think our teachers has marked "none of these" because the shadow formed by translucent objects is VERY light (and hence can be ignored :P).
