Sam ______ his homework in his room now.[ ]
A. does
B. doing
C. is doing
D. do
答案:C
属于债的主体变更的是( )。
A.债的担保方式变更
B.债的标的物数量增加
C.履行期限变更
D.债务承担
防雷措施中,防静电危害的最基本措施是( )。
A.静电中和器 B.接地C.抗静电添加剂 D.增湿