I believe the answer is: C. value of the currencies for two or more countries.
Exchange rate table is usually used in business to compared the cost of buying a certain type of resources from local markets and the foreign markets.
It is also often used by foreign exchange investors to make their speculation in order to make profit from the change in currency's value.
I think Markey systems are the most effective because you sell something and get money pack while others benefit from the item.
Using historical data to make informed decisions about how things may be in the future is an example of making prediction problem domain.
<h3>Problem Domain:</h3>
A problem area is an area of expertise or application that needs to be explored to solve a problem. A problem domain looks only at topics of interest and excludes everything else. This is the area containing the problem that the application is designed to solve.
<h3>What is the problematic domain class?</h3>
In other words, anything substantial found in the domain in question is considered a domain object. In your case you have receptionist, sms, reservation and customer. What we do here is classify (create classes) these objects. This is called a problem domain analysis.
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