A) The medical information
Since 1913, the medical knowledge has vastly changed. Medical terms that are today common-knowledge (DNA, chemotherapy, etc.) were not even in existence in 1913.
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A) the medical information.
If you are consulting a source from 1913, it is very likely that a lot of the information you are going to obtain is going to be outdated. This is because our understanding of the world has changed enormously since that time. However, some information is more likely to be outdated than other. This is the information that has progressed the most, or that changes more quickly. Out of these options, the information that has changed the most is medical information. Therefore, this is the section that is most likely to be outdated.
answer: b. the moon is much smaller than the earth.
it starts off by comparing the earth and venus. it also only says one sentance about the moon which make it the odd one out. in conclusion the answer is b.