The correct answer is: D. The porter said to the lady,”I would take care of your baggage while you bought your ticket.”
The other options are incorrect because they do not use the respectful form of address “Madam.” Option A uses the informal form “I would take care of your baggage while you buy your ticket,” Option B uses the future tense “I will take care of your baggage while you buy your ticket,” and Option C uses the past tense “I would take care of your baggage while you bought your ticket.”
In formal settings, it is customary to address women as “Madam” or “Miss.” The use of the respectful form of address shows that the porter is treating the lady with courtesy and respect.