Right, dangerous isn't exactly what you want, though it's not a bad idea to have it too.
It's a little hard to find unfortunately, but T3 has a global function yesOrNo (look in the symbols index of the Library Reference Manual).
If you're having trouble finding something in the docs another good resource is the old newsgroup. You can search here too of course but the newsgroup has more T3 topics, since it's been around longer, so I usually try that first.
For example, https://groups.google.com/forum/?fromgr ... or$20no%22
And the first hit for that, https://groups.google.com/forum/?fromgr ... 6KY7S0oCIJ
Which would lead you to yesOrNo.
So here's a transcript,
You are carrying an apple.
What do you want to eat?
Are you sure? no
You have second thoughts.
Are you sure? yes
Not only did it look good, it was full of poison.
*** YOU HAVE DIED ***
Would you like to RESTORE a saved position, RESTART the story, see the CREDITS, or QUIT?
IFID = 'foo'
initialPlayerChar = me
startRoom: Room 'The Cottage'
+ me: Actor
++ apple: Food 'apple' 'apple'
"The apple is so pretty, it looks as though it was plucked from the Garden of Eden.
Actually, it looks a little too perfect. "
"Are you sure? ";
if(!yesOrNo()) failCheck('You have second thoughts. ');
"Not only did it look good, it was full of poison. ";