1,再买一张. sunk cost不考虑.当时你能花钱买就证明对你来说CD的utility>$的.除非你的钱少得可怜,否则.再买.

2,hold it. At least you believe in market semi weak form efficiency, so market price must be correct. Your purchase price should not affect your decision of whether to sell the stock or not.

Or, another thought is the riskiness of Microsoft just increase, you might need to reallocate your investment to address this issue.