Let $y=f(x)$ be differentiable. Below are four statements. Select EVERY true statement $($there may be more that one$).$

$y=f^{\text{'}}(xdx)-f^{\text{'}}(x)$

$dy=f(x)dx$

$y=f(xdx)-f(x)$

$dy=f^{\text{'}}(x)dx$