Step 1: the given condition.
We are given \( x<y<z \), meaning \( y \) is the middle value. We are asked to compare the average \( \frac{x + y + z}{3} \) with \( y \).
Step 2: Try an example.
For example, let \( x = 1, y = 2, z = 3 \). Then:
\[
\frac{x + y + z}{3} = \frac{1 + 2 + 3}{3} = 2
\]
Thus, the two quantities are equal in this case. However, if \( x = 1, y = 2, z = 10 \), then:
\[
\frac{x + y + z}{3} = \frac{1 + 2 + 10}{3} = 4.33
\]
Here, Quantity A is greater than Quantity B.
Step 3: Conclusion.
Based on the analysis and the specific examples, the relationship between the quantities can be that Quantity B is greater.
Final Answer:
\[
\boxed{\text{The correct answer is (2) Quantity B is greater.}}
\]