Translation:He showed a great interest in science.
While I understand "great" is the most literal translation, it seems there should be flexibility for other responses that express relative strength or amount. For instance, it would be more natural to say "a big interest" or "a strong interest", at least in my experience.
I put "he showed a great interest for science" and it was rejected. I've done a lot of research on the word 'por' and did not find a meaning of 'in'. Now I realize that you should translate for meaning and I can see how 'in science' fits in this translation, but so should 'for science'. 'For science' and 'in science' is the same meaning in this instance. I reported that my translation should be accepted. We'll see if it actually is.