A:原子序数是9
B:氟是非金属元素
C:质子数是19
D:相对原子质量是19.00
一架天平的游码指在2.5g处,小明同学忘记将游码拨回横梁标尺的零刻度线处就调好平衡了,称量时,物体放在左盘,然后在右盘放了50g砝码后,天平刚好在水平方向平衡,则物体的质量是( )
Now, there are lots of buses and ____.
—Don't play near the classroom, please.
—_______.