Under what condition can an investor execute a short sale according to the Uptick Rule?

The Uptick Rule, which was designed to prevent excessive short selling during market volatility, allows an investor to execute a short sale only when the last sale price of the stock has ticked upward, meaning that it has increased from the previous price. Option B correctly identifies this requirement; specifically, the investor must wait until the price has gone up to place a short sale order. This rule was established to combat manipulation and to stabilize the market by ensuring that short selling does not exacerbate downward price movements.

In contrast, the other options do not align with the conditions set forth by the Uptick Rule. Selling on a downward trend, for example, would be contrary to the rule's objective to prevent further decline in stock prices. A stock less than $10 does not inherently affect the ability to short sell, nor does the valuation of the stock alone determine whether a short sale can occur under the Uptick Rule. Therefore, the stipulation that a price must increase before a short sale can be made is what makes option B the correct choice.