单纯固定液属于剧毒品，是电镜研究的必需固定剂的是（）
A.锇酸
B.三氯醋酸
C.苦味酸
D.醋酸
E.升汞
参考答案：A
I regret _____ you that Tom failed to pass the driving test and that he really regretted ______ your advice on practicing more.
A．to tell; not following
B．to tell; having not followed
C．telling; not to follow
D．telling; not having followed
当变压器的变比小于1时，变压器为（）变压器。
A.升压
B.降压
C.隔离
D.双圈
