A hydraulic jump takes place in a frictionless rectangular channel. The pre-jump depth is $y_p$. The alternate and sequent depths corresponding to $y_p$ are $y_a$ and $y_s$ respectively. The correct relationship among $y_p, \: y_a$ and $y_s$ is:

1. $y_a < y_s < y_p$
2. $y_p < y_s < y_a$
3. $y_p < y_s = y_a$
4. $y_p = y_s = y_a$