In What Way Did Optical Illusion Mislead Earlier Visual Observers

In what way did optical illusion mislead earlier visual observers of Mars?

A) Chance alignments of faint dark features looked like manufactured canals, and variable dark areas near the equator were interpreted as vegetation.
B) Moving areas of obscured detail on the planet were interpreted as massive flash floods rather than dust storms.
C) Apparent movement of surface features due to seeing fluctuations of images when viewed through Earth's atmosphere were interpreted as evidence of movement of life-forms, or Martians.
D) Volcano structures were seen as eye-shaped images and were interpreted as having been made by intelligent beings to indicate their presence on Mars.