B. The Difficulty I Met with My Granddad

C. The First Time I Got My Own Bike

D. The Great Moment When I Stayed with My Granddad

　　　　　　　　　　　　　　　　　　C

　　The loud noise of the cars or the sound of a plane can force its way into the deepest forest, yet it's not only humans that are bothered by the noise.

　　Bioacoustician Bernie Krause has been studying the effect of noise pollution on wildlife, and has come across some interesting behaviors, especially among animals that communicate by sound, like humans. Birds use sound to communicate, but in noisy places, these animals have to shout over the natural noise to be heard.

　　Krause mentions a study of nightingales(夜莺) to explain what he means. The birds responded to（回应） traffic noise by singing louder and louder until they actually went beyond noise pollution standards in the city. To belt out (sing loudly) their songs, they increased their lung pressure fivefold, but scientists say that this is not dangerous for the birds themselves.

　　Studies show that sudden noise can cause certain birds to leave their nests, leaving the young to their enemies. One study also showed that songbirds that nested close to busy motorways were much less productive than those that nested farther away. Mammals（哺乳动物）too are affected(影响). A recent study showed that nursing caribou（驯鹿） responded to plane noise by not producing enough milk to feed their young.

In some cases noise pollution can actually help some animals while harming others. Toads（蟾蜍）and frogs are known to sing in union（同步发声）so that no predator (their enemies) can catch them. Krause found that when planes flew overhead and disturbed the toad's song, they lost their union, and it took them 45 minutes to get it back again. That gave their natural enemies plenty of time to find