16.Heart disease takes up about__________of the in-flight medical emergencies on US flights.

　　A) 13%

　　B) 460/o

　　C) 18%

　　D) 6%

　　17.According to the passage, the expansion of air in body cavities can result in____________.

　　A) heart attack

　　B) chest pain

　　C) stomach cramping

　　D) difficult breathing

　　18.According to the passage, why does deep venous thrombosis usually happen?

　　A) Because the economy class is not spacious enough.

　　B) Because there are too many economy-class passengers.

　　C) Because passengers are not allowed to walk during the flight.

　　D) Because the low pressure in the cabin prevents blood flowing smoothly.

　　19.According to the J998 Aviation Medical Assistance Act, Doctors who came to passengers' aid__________.

　　A) do not have to be worried even if they give the patients improper treatment

　　B) will not be submitted to legal responsibility even if the patients didn't recover

　　C) are assisted by advanced emergency medical kits

　　D) will be greatly respected by the patient and the crew

　　20.The phrase "getting winded" (Line 2. Para. 5) is closest in meaning to____________.

　　A) falling over

　　B) being out of breath

　　C) spraining the ankle

　　D) moving in a curving line