The study estimated that there are a(n) 【C9】______ of 30 in-flight medical emergencies on U.S. flights every day. Most of them are not 【C10】______ fainting and dizziness are the most frequent complaints. 【C11】______ 13% of them— roughly four a day are serious enough to 【C12】______ a pilot to change course. The most common of the serious emergencies 【C13】______ heart trouble, strokes, and difficulty breathing.
Let's face it: plane rides are 【C14】______ . For starters, cabin pressures at high altitudes are set at roughly 【C15】______ they would be if you lived at 5,000 to 8,000 feet above sea level. Most people can tolerate these pressures pretty 【C16】______ , but passengers with heart disease 【C17】______ experience chest pains as result of the reduced amount of oxygen flowing through their blood. 【C18】______ common in- flight problem is deep venous thrombosis— the so-called economy class syndrome (综合症). 【C19】______ happens, don't panic. Things are getting better on the in-flight- emergency front. Thanks to more recent legislation, flights with at 【C20】______ one attendant are starting to install emergency medical kits to treat heart attacks.
【C1】

A. called
B. addressed
C. informed
D. surveyed