Find the greatest common factor of these three expressions. \[ 28 y^{2}, 42 y^{5}, \text { and } 70 y \]

Step 1 ：Find the GCF of the coefficients 28, 42, and 70. The greatest common factor of these three numbers is 14.

Step 2 ：Find the lowest power of y in the three expressions 2, 5, and 1. The lowest of these is 1.

Step 3 ：Therefore, the greatest common factor of the three expressions is \(14y\).

Step 4 ：So, the final answer is \(\boxed{14y}\).