GRE question: oscilloscope with two oscillators

[Silviu]

Homework Statement

Hello! The problem is the one I attached.

Homework Equations

The Attempt at a Solution

They say the answer is A, but I am not sure why. From what I remember from lab class, when you put 2 signals on x and y-axis you get usually a closed loop, like D or E. I think D happens when you have the same frequency but different amplitudes so I assumed the answer is E. Can someone explain why is it A?

Thank you.

 

[DrClaude]

In E, what would be the relative frequencies along X and Y?

 

[Silviu]

In E, what would be the relative frequencies along X and Y?

Oh, I am not sure. I picked that just by elimination...

 

[vela]

How did you eliminate the others then?