Ann is visiting Paris. She will/is going to see the Eiffel Tower.

English Explanation:

'Ann is visiting Paris. She is going to see the Eiffel Tower' uses 'is going to' to express a planned future action that is very likely to happen, especially since she is already visiting Paris. 'She will see the Eiffel Tower' could be used if the decision to see it is made at the moment of speaking, or as a simple statement of a future event. Given Ann is visiting Paris, seeing the Eiffel Tower is a highly probable part of her itinerary, making 'is going to' a strong choice.