通常情况下，挂篮锚固系统精轧螺纹钢宜用（）锁紧
A.单螺母
B.双螺母
C.双螺母
D.四螺母
参考答案：B
Mrs Smith had to ______ her father day and night because he was seriously ill.
A. look at B. look like C. look after
图标中对图样中除角度以外的尺寸的标注已纺一以（）为单位。
A、厘米
B、英寸
C、毫米
D、米
