How to change x axes' range

From: Qin Liu

Hi, there:

When plot ann predicted results I need to indicate numbers of 
inputs for
each column. 

        V1       V2         V3          V4
1  86.2700  49.9380  30.7630  0.1327
2  89.5127  55.9707  33.7683  0.1186
3  91.1833  58.4670  34.5610  0.1134

matplot(t, pch = 1:4, type = "o", col = rainbow(ncol(t)),xlab 
= "No. of
inputs ",  ylab = "Mean of 6 Datasets", main = "xxxxxxxxxxx")

Instead of have typical x axes' range as "1, 2, 3, and 4" for 
each column, I
need to indicate "11 Vars, 10 Vars, 6Vars, and 4Vars" or "A, 
B, C, and D"

Does anybody know anything about it? I appreciate if you 
could help me out.

Thank you very much indeed.

Qin