Why Do Some Scientists Think That the Idea of the Habitable

Why do some scientists think that the idea of the habitable zone as a fixed distance range from a star is too restrictive?

A) Changes in stars' brightness might change the position of habitable zones.
B) Many forms of life do not require liquid water.
C) Planets may not always keep a constant distance from their star.
D) Liquid water can be maintained by tidal heating.