English teachers are supposed ________ their students a test in class, even after class, ________ better teaching results.

A．to give; ensuring

B．giving; to ensure

C．to give; to ensure

D．giving; ensuring

下列哪项不属于环境对磁场的影响范畴()

A．地板内的钢筋网

B．大功率电缆变压器

C．轮椅担架

D．小汽车、卡车

E．心脏起搏器离子泵等体内植入物