Which of the following statements about the Greek letters of an option are correct?(multiple answers)

OA put option's theta is always positive.OAn option's gamma is a source of risk that cannot be hedged by using a position in the underlying asset.DA put option's delta is close to O when the option is deep out-of-the-money.O An option's vega is the rate of change of the option's value with regards to the volatility.OA call option's gamma is always positive.