We accept the claim. This comes from the fact that if there is no mechanical assistance after point A (that is the tallest) then we make sure that the potential energy converts in kinetic energy and that way we make sure that the rollercoaester reaches all the other hills. If the tallest point is not the first one and there's no mechanical assitances then the rollercoester won't reach the hills that are taller than the first one (the kinetic energy won't be enough to reach it).