The Put-Call parity for European options written on non-dividend paying assets, roughly speaking, states that:

Select one:

a. As the source of risk in both options is the same, the price of one option can be determined by adequately combining the underlying asset, the risk-free asset and the other option.

b. PUT and CALL options come in pairs, that is: to every PUT option, there is a corresponding CALL option, and vice versa.

c. If market participants are risk-neutral, both options should be worth the same, because the possibility that the underlying asset price rises is equal to the possibility that it decreases.

d. As a PUT option gives its holder the right to sell and a CALL option the right to buy, their prices must be equal, since the purchase price must equal the sale price.