为明确诊断，下列哪项检查为首选
A．心电图B．超声心动图C．24小时动态心电图D．心功能检查E．心导管检查
参考答案：B
染色体是成对存在的，基因也是成对存在的______．
He was educated at a local grammar school, _______ he went on to Cambridge.
A．from which
B．after that
C．after which
D．from this
