The most suitable word to fill the gap in the passage is a) conveyed.
So, the completed sentence would read: "This is a formal occasion on which speeches are made reaffirming the friendly relations and spirits of conveyed."
The word "conveyed" fits well in the context of reaffirming relations, suggesting that friendly sentiments and relationships are expressed or transmitted during the occasion. However, if you were looking for a word that describes who is being referred to in terms of relations (such as nations or groups), then "empowered" could also fit, but the sentence structure seems to favor "conveyed" more.
If you meant to capture a specific context of empowerment or official recognition, "accredited" could also be a fit depending on the broader context of the passage. It would help to know more about the overall content of the passage for the most accurate choice.
In summary, the best choice given the options is a) conveyed.