18 of 30 An increase in which of the following will increase the value of an American call option? 1. Dividend payments of the underlying asset 2. Rate of risk-free asset 3. Time to expiration 4. Variance of the return on the underlying asset O a. 2,3,4 are correct O b. All are correct O c. 1,2,4 are correct Od. 1,3,4 are correct O e 1,2,3 are correct