切割非金属材料用的等离子弧形式采用()。
A．非转移型弧
B．转移型弧
C．正接型弧
D．反接型弧
参考答案：A
By the time he showed up, we _ _ twenty trees. [ ]
A. has planted
B. have planted
C. had planted
D. were planting
经皮给药适用于哪些药物（）
A.分子量小
B.药理作用强
C.剂量大
D.非极性强
E.既有一定脂溶性又有一定水溶性
