C. The score of New York’s taxis this year is lower that of last year.

　　D. The global big cities’ taxis service is scored by a travel website every year.

　　D

　　The rising level of noise in urban areas may be preventing some species of songbirds from setting up homes in developed areas, a study has concluded.

　　Canadian researchers found that noisy surroundings masked the lower frequencies of bird songs, affecting the way some species communicated. Unable to hear all elements of a song, females tended to regard singing males as ill-suited mates(配偶).

　　“We sometimes find areas within cities that have what seem like suitable habitats, yet we get less diversity (of songbirds). So we wanted to investigate whether there was link between bird diversity and noise levels or not,” said co-author Darren Proppe at Calvin College, US.

　　In order to do this, the team surveyed species at 113 sites in natural areas within the city of Edmonton. What they found was that the number of species at each location tended to be lower when noise levels were higher.

　　The study also focused on seven species that did inhabit the areas to see if their abundance was affected as urban noise increased. The species that were selected met a number of criteria, including relative commonness across the study area and forest or forest-edge dwelling (住处).

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