D is correct: since there is no relationship between ExchangeRates and Sales, LOOKUPVALUE is the appropriate DAX function to retrieve a scalar value from ExchangeRates based on the currently selected currency. MAX(Currency[CurrencyCode]) retrieves the single currency code in the current filter context (from a Currency slicer), and LOOKUPVALUE fetches the corresponding rate from ExchangeRates. Multiplying by SUM(Sales[Amount]) gives the converted total. A is wrong: RELATED is a row-context function used in calculated columns to traverse a relationship — it cannot be used in a measure context and requires an existing active relationship. B is wrong: USERELATIONSHIP activates an existing inactive relationship; it cannot create a relationship that does not exist in the model, and it is used inside CALCULATE for measure filters, not for arithmetic multiplication. C is wrong: SUMX with LOOKUPVALUE per row would work correctly in some scenarios, but it is inefficient for this use case because it performs a row-by-row lookup on the entire Sales table. Additionally, if all Sales[Amount] values are in USD and the exchange rate is a single scalar per selected currency, the row-level lookup is unnecessary. D is more efficient. E is wrong: TREATAS maps a table's columns to behave like another table's columns for filter propagation; it does not retrieve a scalar rate for multiplication and would not produce the desired calculation.