Which of the following statements is true, all else equal?

An increase in the stock price will cause an increase in the call price but cause a decrease in the put price.

For puts, but not calls, an increase in the time to expiration will cause an increase in the option price.

An increase in the exercise price will cause an increase in put price but cause a decrease in the call price.

For both calls and puts, an increase in the stock price volatility will cause a decrease in the option price.

Both a and c.