The Eiffel Tower can be fifteen centimeters taller during the summer due to thermal expansion of the iron.
Why it is true
Summer heat causes the iron in the structure to expand, increasing the total height of the monument, while in winter the metal contracts and the tower shrinks slightly.
Source: Engineering
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.