Teachers must put the brakes on,as it were,when they notice students looking puzzled.请问这句话的语法结构如何理解?look为什么要加ing?

Teachers must put the brakes on,as it were,when they notice students looking puzzled.请问这句话的语法结构如何理解?look为什么要加ing? Teachers'Day is on september 10th.改错 September 10th is ( ) Teachers'Day.A.the B./ 翻译：We put on performances for parents and teachers. September 10th is( Teachers' Day.)对括号提问.（ ） （ ）is September 10th? I must put everything in order . l must put the______in the bin I MUST PUT THE PLAN INTO PRACTICE! open natural smile,must put down garments. We must listen our teachers carefully in class.改错 Students must listen carrfully and f_____ teachers in class. We must listen to our teachers.改成同义句. teachers must take care of the students改为被动语态 ----------------------（众所周知）,we must depend on teachers to acqui Teachers‘s Day is （on September 10th）.对括号部分提问 （ ）（ ）（ ）Teachers’Day? the L/C must be opened before August 26th. When is__Day?It's on__A.Woman's;March 8th B.Mothers';the second Sunday of May C.Teacher's;October 9th D.Teachers';September 10th All the ____(woman)teachers enjoy themselves on March 8th every year.