Which lens for portraits?

I'm new to DSLRs. The K5 is my first one. I'm going to an indoor evening tutorial on portrait photography. The professional is supplying the models and lighting. I only want to take one lens and my choices are 18-135 WR; 50-200 WR; DA 35mm 2.4 AL. The later two were purchased recently on this forum. Which lens should I put on the camera?
All/any advice would be appreciated.

If you want to maximise your learning from this, I would suggest you take all three lenses and see what works best for you.

It is likely that you will be using studio flash, so in terms of aperture maybe f8 or f11 will be appropriate, so if so all the lenses are capable of that.

To be honest, taking a kit of three lenses to a studio doesn't seem too onerous.

Thanks John,
The reason I only wanted to take one is that there will be quite a few people there and I don't like leaving kit lying around. It's not a studio more a church hall. Maybe I've previously mixed in the wrong crowds!

Photographers are a pretty honest bunch of people, but I understand.

In that case, the 18-135mm will cover the most eventualities!

18-135mm and the 35mm is small enough to keep in a pocket.

unfortunately that doesn't work the other way, if eventually Frank change the lenses....

it isn't a question of which lens.. it is a question of what camera bag... the lowpro sling bag makes lens changes easy and you don't have to leave anything layin around where it might get stolen..

DOH!

Thanks a lot for the advice. I'll stick with the 18-135. It was nice of you all to take the time to reply.

I'd take the 50-200

I only bought the 50-200 because I needed to reassure myself that I'd made the right kit lens choice, which I think I did. I do a lot of walking in rough terrain and if I fall its more expendable. Why would you choose the 50-200 Ken?