A:3.2×10–19 C
B:–6.4×10–19 C
C:–1.6×10–18 C
D:4.0×10–19 C
You'd better ask a ______, such as your aunt or sister, to look after your children while you are away.
预计下届世博会将吸引约69000000人次参观,将69000000用科学记数法表示正确的是( )
如果你想说“让我们一起唱首生日快乐歌”,你应该怎么说?