Suppose I have a macro like this:

\define[1]\thisismylist{
This list has n items.
\startitemize   #1\stopitemize

}

And in the document it might have this:
\thisismylist{\item cat\item dog\item tree
}
How can I make n display three, as there are three items?
"This list has 3 items:
1. cat2. dog3. tree
I will use this as a means to check if the description before a list needs a plural or not:
Read the prompts below:
- Do you think cats should be banned from university dormitories?- Should public schools provide free breakfast?

And that way, if there is only one prompt, it changes the instructions to be:
Read the prompt below:
- Do you think cats should be banned from university dormitories?

--Joel