The combination of temperature and pressure ________the densities become equal is called the critical point.
句意： 温度和压强的密度达到相同点的组合被称作临界点。 句中的先行项为 the combination of temperature and pressure， 关系从句的范围仅到 equal 而不是句末， 先行项在关系从句中作主语； 关系从句还原为：The densities become equal at the combination of temperature and pressure.