New Colum in Choice index table

Hello,
I'm trying toadda newcolumn to the tablethat showsthe selectionswithyour answersand I have aproblem whenaddinga newhead.
In the filemod/ choice/index.phpis setas follows:
$ table-> head= array($strsectionname,get_string("question"),get_string("answer"));

And I want toadd anothertype:
$ table-> head= array($strsectionname,get_string("question"),get_string("answer"),get_string("intro"));

but I getinMoodleas follows:

Question Answer[[intro]]

Knowto bethe problem?

I useversion 2.3.

thank you very much