妈妈对着吠叫的小狗发出'嘘嘘嘘嘘嘘'声让它安静下来。

Mom made a ___sh-sh-sh-sh-sh sound to quiet the barking puppy.

老师走进来时，同学们立刻发出'嘘嘘声'提醒彼此安静。

When the teacher entered, the students immediately made '___sh-sh-sh-sh-sh' sounds to remind each other to be quiet.