It's hard to hold back the tears．This is ______thing I've ever heard．
物质
实验序号
体积（厘米3）
质量（克）
甲
1
10
8
2
20
16
3
30
24
4
40
32
乙
5
27
6
54
7
81
108
—I want to see Mr. White. We have an appointment.
—I'm sorry, but he is not ________ at the moment, for the meeting hasn't ended.
