Answer:
The correct answer is letter "D": multiple systematic risk factors.
Explanation:
The Arbitrage Pricing Theory or APT weights the influence of different macroeconomic factors on an asset return. If the asset's price is different than the model's projection an opportunistic investor can buy and sell the asset for a profit. Those macroeconomic factors can include economic output, unemployment, inflation, savings or investments-specific considerations and they capture systematic risk.