肺内错构瘤的特征性X线表现是（）
A.孤立圆形阴影
B.肿块边缘清楚
C.肿块边缘可分叶
D.肿块内见爆米花样钙化
E.肿块内可形成空洞
参考答案：D
An investor buys 200 shares of ABC at the market price of $100 on full margin. The initial margin requirement is 40 percent and the maintenance margin requirement is 25 percent. If the shares of stock later sold for $ 200 per share, what is the rate of return on the margin transaction（）
A. 250%.
B. 100%.
C. 200%.
直流电弧焊时，焊件接电焊机输出端的正极，焊枪接输出端的负极的接线法，叫（）接法。
