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.