A:Do you have
B:Did you have
C:Have you had
D:Had you had
物质
甲
乙
丙
丁
反应前物质质量/g
8
32
5
4
反应后物质质量/g
16
x
24
There aren't many tickets left for the concert. You'd better (你最好 ) __________ that you get one today.