Q15

[Johnschneringer]

I do not understand why the answer is D. Isnt it true that neither T or Q could go first?

[demetri.blaisdell]

Thanks for posting. Be careful with the QT constraint. Q can't come before T. But that still allows them to appear together in the same period (Q wouldn't be before if they were from the same period). So I think the possibilities for TQ are:

1) TQ VS ZR or
2) T can go in the first pair and Q can go in either of the other pairs or
3) T can go in the middle pair and Q can go in the last pair

If Q and T can appear in the first period, that knocks off (A) and (B).

So who else can't be in the first period? That's V and Z. That knocks of (E).

We're left with (C) and (D). The only question is whether R can appear there. Let's try it out.

QR VS TZ looks OK to me.

That QT constraint is tricky but it's the kind of thing that comes up a lot. I hope this helps. Take another look at the diagram that Noah posted on the forums. Let me know if you have any questions.

Demetri