下列自然现象中,属于液化现象的是( )
— Would you like______to the park with me?—I'd love to, but I must do my homework first.
桦树林中出现了一些云杉的幼苗,云杉长大后,其高度超过桦树,桦树因不耐阴而逐渐死亡,桦树林最终被云杉取代.这一变化过程表明( )