His father enjoys ____ a walk after dinner.[ ]
A. takes
B. take
C. taking
D. to take
答案:C
几何体的下列性质:①侧面是平行四边形,②底面形状相同,③底面平行,④棱长相等,其中是柱体的性质的有[ ]
A.1个
B.2个
C.3个
D.4个
变压器的效率是输出功率与输入功率之比的百分数