植物体能够由小长大,主要依靠细胞的____使细胞数目增多,其次是依靠细胞的____使体积增大.
①三个氢氧根离子____②干冰____ ③汞元素____.
— John, could you please the black-board now? It's your duty today.— OK. I'll do it right away.