It is a process of representing graphics objects a collection of pixels. The graphics objects are continuous. The pixels used are discrete. Each pixel can have either on or off state.
A. Aliasing effect occurs due to to bad sampling of scan lines over the object , which is occure due to discontinuity of objects and scanning is reffered at integer value.
B. Unequal Intensity occures due to uneven brightness of object during scan conversion.
C.During scan conversion same pixels may be drawn multiple times , is known as overstriking
D. Local and global aliasing are also cause by scan conversion
So Answer is D