Match the code on the left with the precondition $P(x,y)$ and postcondition $Q(x,y)$ on the right that verifies its correctness.

Instructions

$t$:$=x$

$x$:$=2y$

$y=2t$

$t$:$=x$

$x$:$=y^2$

$y=t$

$t$:$=x$

$x$:$=y+2$

$y=t$

$t$:$=x$

$x$:$=y+2$

$y=2t$

Precondition: $P(x,y)$ is the statement $"x=$a and $y=b"$

Postcondition: $Q(x,y)$ is the statement $"y=2$a and $x=2b^n$

Precondition: $P(x,y)$ is the statement $"x=$a and $y=b"$

Postcondition: $Q(x,y)$ is the statement $"y=$a and $x=b+2"$

Precondition: $P(x,y)$ is the statement $"x=$a and $y=b"$ Postcondition: $Q(x,y)$ is the statement $"y=2$a and $x=b+2"$