7+1=8(本)
答:需要8本集邮册才能把这些邮票插完。
物质
a
b
c
d
反应前的质量(g)
7.4
4.2
5.0
3.8
反应后的质量(g)
6.2
x
8.2
I hate it when she calls me at work—I'm always too busy to _____ a conversation with her.