{"answers": "D", "options": ["f : great . the light of the sun can tell us how old it is .", "f : that is true . we can know the age of a tree from its size .", "f : yes . from the color of a tree , we can figure out how old it is .", "f : you are right . people can know the age of a star from its size ."], "article": "f : how do you know how old a star is ? m : for most stars , we find its age from how big it is . we can know its size from the amount of light it puts out and its color . then the size tells us how long a star will live . big stars live a short life , while small stars live much longer .", "id": "train_3057"}