Given:
Quantity A: 2x - z
Quantity B: -y

Let's try to make the quantities RESEMBLE the given inequality: x + y < z

Add y both quantities to get:
Quantity A: 2x - z + y
Quantity B: 0

Add z both quantities to get:
Quantity A: 2x + y
Quantity B: z

SO CLOSE!!
If Quantity A were x + y (rather than 2x + y), we'd be able to conclude that Quantity B is bigger (since we know that x + y < z)
HOWEVER, this is not the case.

Given all of this, it seems likely that the correct answer might be D.

So, let's test some possible values of x, y and z (that satisfies the restriction that x + y < z)

case i: x = 3, y = 1 and z = 5 (this satisfies the inequality x + y < z)
We get:
Quantity A: 2x + y = 2(3) + 1 = 7
Quantity B: z = 5
In this case, Quantity A is greater

case ii: x = 3, y = 1 and z = 500 (this satisfies the inequality x + y < z)
We get:
Quantity A: 2x + y = 2(3) + 1 = 7
Quantity B: z = 500
In this case, Quantity B is greater

Answer: D

Cheers,
Brent