仪器在起下过程中产生螺纹脱扣的原因？

Even though it was only October，my students were already whispering about Christmas plans. With each passing day everyone became more____ waiting for the final school bell. Upon its____  everyone would run for their coats and go home，everyone except David.
David was a small boy in ragged clothes. I had often____ what kind of home life David had，and what kind of mother could send her son to school dressed so____for the cold winter months without a coat，boots，or gloves. But something made David____.I can still remember he was always____a smile and willing to help. He always____ after school to straighten chairs and mop the floor. We never talked much.He____ just simply smile and ask what else he could do，then thank me for letting him stay and slowly____ home.
Weeks passed and the____ over the coming Christmas grew into restlessness until the last day of____ before the holiday break. I smiled in____ as the last of them hurried out of the door. Turning around I saw David____ standing by my desk.
“I have something for you，”he said and____from behind his back a small box.__ __  it to me，he said anxiously，“Open it.” I took the box from him，thanked him and slowly unwrapped it. I lifted the lid and to my____ I saw nothing. I looked at David’s smiling face and back into the box and said，“The box is nice，David，but it’s____.”
“Oh，no. It isn’t.” said David.” It’s full of love. My mum told me before she died that love was something you couldn’t see or touch unless you know it’s there.”
Tears filled my eyes_____  I looked at the proud dirty face that I had rarely given____ to. After that Christmas，David and I became good friends and I never forgot the meaning____the little empty box set on my desk..

小题1:	A．cautious B．courageous C．serious D．anxious

小题2:	A．warning B．calling C．ringing D．yelling

小题3:	A．scolded B．wondered C．realized D．learned

小题4:	A．modestly B．naturally C．inaccurately D．inappropriately

小题5:	A．special B．upset C．popular D．funny

小题6:	A．wearing B．delivering C．expressing D．sharing

小题7:	A．practised B．wandered C．studied D．stayed

小题8:	A．might B．should C．would D．could

小题9:	A．aim at B．head for C．put off D．turn to

小题10:

A．argument B．judgment C．movement D．excitement

小题11:

A．education B．year C．school D．program

小题12:

A．relief B．return C．vain D．control

小题13:

A．weakly B．quietly C．sadly D．helplessly

小题14:

A．searched B．found C．raised D．pulled

小题15:

A．Holding B．Handing C．Sending D．Leaving

小题16:

A．appreciation B．expectation C．delight D．surprise

小题17:

A．empty B．cheap C．useless D．improper

小题18:

A．as B．until C．because D．though

小题19:

A．advice B．support C．attention D．command

小题20:

A．from B．towards C．over D．behind