Answer: B. The investor has a short-term capital loss of $20,000.
Step-by-step explanation:
A short-term loss occurs when a deficit is realized when there's a sale of an asset which has been held by the person for a period of one year or less.
In this case, since the security was worthless, it's a loss and was also help for six months which is less than one year, then it's a short term capital loss.
Therefore, the correct option is B