A rat or pigeon might not be the obvious choice to tend to someone who is sick, but th

Pigeons are often seen as dirty birds and an urban__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 accuratethe rats are able to find more TB infections and, therefore, save more lives.

A) associatedI) slight

B) examine

C) indicate

D) nuisance

E) peak

F) preventing

G) prohibiting

H) sensitive

I) slight

J) specify

K) superior

L) suspicious

M) tip

N) treated

O) visual