已知粉笔盒里只有2支黄色粉笔和3支红色粉笔,每支粉笔除颜色外均相同,现从中任取一支粉笔,则取出黄色粉笔的概率是( )
A:15
B:25
C:35
D:23
下列关于胶体的叙述不正确的是( )
a(1)=False
For i = 2 To 20
a(i) = True
Next i
If a(i) = True Then
For j = 2 To 20 \ i
a(i * j) = False
Next j
End If
t = 0
For i = 1 To 20
t = t + 1
经过该程序段运行后,变量t的值为( )