张明老师在探究燃烧的条件时,改进了教材中的实验装置:在铜片上罩了仪器a.
(1)仪器a的名称是____.
(2)罩上仪器a的作用是____ .
(3)由①和③实验事实,能够获得可燃物燃烧需要的条件之一是____.
(4)热水在实验中的作用是____ 和____ .
I worked hard and ____ ____ ____ ____ my teachers and classmates.
一 I have made great progress in spoken English since last year.
一 Well done! I am sure you'll be good at it soon.
关于声现象下列说法错误的是( )