题目内容：
(49)__________
A．So far, we have not known exactty yet whether mouth-to-mouth breathing is really useless in CPR. B．Only ten percent of the victims treated with traditional CPR survived with good brain ability.
C．CPR keeps blood and oxygen flowing to the heart and brain.
D．His studies show that many people do not want to perform mouth-to-mouth breathing on a stranger for fear of getting a disease.
E．It said people should increase the number of chest presses from fifteen to thirty for every two breaths given.
F．No mouth-to-mouth rescue breaths were given to them.
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