Answer:
A. Exercise price
Step-by-step explanation:
The following explanations should help.
Opening price is the price at which an asset trades when the market position opens, usually at the start of the day. This is not a fixed price and as such may change over different days.
Spot price and market price are identical, these are the prices that are currently prevailing in the market. This is the price that can be obtained by selling or purchasing the asset right now in the market.
Exercise price is the price an investor can execute and claim any time when the market position favors them to obtain a profit. This is the price in the underlying contract when an investor buys an option contract. A fixed price that can be used to exercise the option any time.
Hope that helps.