A:接头安装噪声监测器
B:道路两旁设置隔音板
C:学校附近禁止鸣笛
D:飞机旁工作人员佩戴耳罩
油菜花有____萼片、____花瓣、____雄蕊、____雌蕊。
( 1 ) {2m−n=1m+n=2 (2) {x−2y=3y+z=1 (3) {x=1x+2y=5 (4) {x2+y=5x−y=4 .
Jack not only enjoys playing football but also enjoys playing flute.
下面哪种物质是固体( )