胎儿脐带的超声图像特征是:( )① 一端连接胎盘,一端连接胎儿脐部;② 横切呈“品”形;③ 纵切呈麻花样;④ 多普勒超声显示1条脐静脉和2条脐动脉
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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