If a star that is 10 million years old will end its life in a supernova in 50 million years, has the supernova already occurred?

The correct understanding of this scenario involves considering the timelines associated with the star's life. If the star is currently 10 million years old and it is expected to go supernova in 50 million years, this means that the supernova event will actually take place when the star reaches an age of 60 million years (10 million years + 50 million years).

Thus, when considering the question of whether the supernova has already occurred, it's clear that since the star has only lived for 10 million years so far, it is far from reaching the age at which it will undergo its supernova phase. Therefore, it makes sense to conclude that the supernova event has not yet happened, as it will only occur in 50 million years, making the star 60 million years old at that point.

This aligns with the choice indicated, as it accurately reflects the aging process of the star and its future states. Meanwhile, options that suggest the supernova has already occurred misunderstand the timeline and sequence of events relative to the star's life cycle.