题目内容：
回答题：Drug Reactions — a Major Cause of Death
Adverse drug reactions may cause the deaths of over 100,000 US hospital patients each year, making them a leading cause of death nationwide1, according to a report in the Journal of the American Medical Association.
“The incidence of serious and fatal adverse drug reactions (ADRs) in US hospitals was found to be extremely high,” say researchers at the University of Toronto in Ontario, Canada.
They carried on an analysis of 39 ADR-related studies2 at US hospitals over the past 30 years and defined an ADR as “any harmful, unintended, and undesired effect of a drug which occurs at doses used in humans for prevention, diagnosis, or therapy.”3
An average 6.7% of all hospitalized patients experience an ADR every year, according to the reasearchers.They estimate that "in 1994, overall 2，216 000 hospitalized patients had serious ADRs, and 106,000 had fatal ADRs." This means that ADRs may rank as the fourth single largest cause of death in America.4
And these incidence figures are probably conservative, the researchers add, since their ADR definition did not include outcomes linked to problems in drug administration, overdoses, drug abuse, and therapeutic failures5.
The control of ADRs also means spending more money. One US study estimated the overall cost of treating ADRs at up to $4 billion per year.
Dr. David Bates of Brigham and Women's Hospital in Boston, Massachusetts, believes that healthcare workers need to pay more attention to the problem, especially since many ADRs are easily preventable. "When a patient develops an allergy or sensitivity, it is often not recorded,"Bates notes6, "and patients receive drugs to which they have known allergies or sensitivities with disturbing frequency.”7 He. believes computerized surveillance systems still works-in-progress at many of the nation's hospitals8 — should help cut down the frequency of these types of errors.
Researchers at the University of Toronto believe that _________. A．ADRs have caused medical problems, though they seldom lead to death.
B．ADRs have very often caused patients to die in Canada.
C．ADRs have caused many deaths in America over the past 30 years.
D．it is easy to prevent ADRs from happening.
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