Translation:My younger brother is living in London this year.
Some inconsistency here, many other earlier courses allow you to just write brother in place of "older brother/younger brother". However, in this translation, it is rejected.
I know taking it very literally it should be a younger brother but in Chinese, you are forced into daily language to use one of these words. Whereas in English you are not forced to distinguish between younger and older (hence why the answer is accepted elsewhere on Duolingo).