关于short selling, sold short英文的用法~

1. Someone is doing the short selling on a stock.
2. Someone sold short a stock.

3. Someone short sold a stock

4. Someone is shorting sell on a stock.

5. If someone shorts sell this stock now,........

请问以上那句话是对的，还是说都不对？如果都不正确，怎样是正确的表达方式？谢谢！

之前做过一段时间portfolio management,也作过short sell.
用的时候直接用short or go short
ex. someone goes short on the stock
someone shorts on the stock
short selling 做名词用. shortselling is a trading strategy.