breaking command in command line in R for Mac Aqua

I'm using R for Mac Aqua version 2.1.1

If at the command line, I type:
ls(
and then a return, the command line prompt changes to
a plus sign indicating that the command has not been
completed.  How do I break, or kill, the partial
command?  Sometimes, I type a long command but miss a
bracket or parenthesis.  On a unix or linux version of
R, I can type ctrl-c.  On the Mac, ctrl-c,
command-(dot), and escape do not work.

Any solutions?
Mike