Asset Price Bubbles Occur Because

Asset price bubbles occur because:

A) Of a global imbalance in assets.
B) The supply of assets falls at a faster rate than the demand thus creating a shortage.
C) Expectations of price movements are factored in as a result of the rise in global asset levels.
D) Asset traders become more risk averse over time.
E) Regulators take insufficient notice of the supply and demand of global assets.