2017年12月四级 Part III Reading Comprehension ( 40 minutes ) Section A Directions: In this section, there is a passage with ten blanks. You are required to select one word for each blank from a list of choices given in a word bank following the passage. Read the passage through carefully before your choices. Each choice in the bank is identified by a letter. Please mark the corresponding letter for each item on Answer Sheet 2 with a single line through the centre. You may not use any of the words in the bank more than once. A rat or pigeon might not be the obvious choice to tend to someone who is sick, but these creatures have some ##26## skills that could help the treatment of human diseases. Pigeons are often seen as dirty birds and an ##27## , but they are just the latest in a long line of animals that have been found to have abilities to help humans. Despite having a brain no bigger than the ##28## of your index finger, pigeons have a very impressive ##29## memory. Recently it was shown that they could be trained to be as accurate as humans at detecting breast cancer in images. Rats are often ##30## with spreading disease rather than ##31## it, but this long-tailed animal is highly ##32## . Inside a rat's nose are up to 1,000 different types of olfactory receptors ( 嗅觉感受器 ), whereas humans only have 100 to 200 types. This gives rats the ability to detect ##33## smells. As a result, some rats are being put to work to detect TB( 肺结核 ). When the rats detect the smell, they stop and rub their legs to ##34## a sample is infected. Traditionally, a hundred samples would take lab technicians more than two days to ##35## , but for a rat it takes less than 20 minutes. This rat detection method doesn't rely on specialist equipment. It is also more accurate — the rats are able to find more TB infections and, therefore, save more lives.