请在收据上签名确认。

Please ___sign the receipt to confirm.

老师向听障学生解释了这个概念。

The teacher ___explained the concept to the hearing-impaired student.

老师用手势示意同学们安静下来。

The teacher ___signaled for the students to quiet down.

这家公司刚刚签下了三位经验丰富的工程师。

The company just ___signed three experienced engineers.