He often __________emails to his parents on weekends.
用平底锅烙饼，每次最多只能烙2张饼，两面都要烙，每面3分钟．烙4张饼最快用（ ）完成．
（Ⅰ）求此几何体的体积；
（Ⅱ）求证：平面PAE⊥平面PDE．
名著阅读。
