[R] how to draw an overlaid plot for multiple curves using different symbols for each curve?

[Sun]

Hello, Rusers:

I have a question to ask for your help. The data has three columns: a, b and
c.

We need to draw an overlaid plot of curves of "a" versus "b" for different
c. That is, draw many curves in one plot and each curve uses a different
symbol.

Does R have such functions? I have searched for a while. But seems not. I am
new to R. Your help is highly appreciated.

Many thanks. Looking forward to your response,

Sun