根据所列微粒：HF、H₂O、NH₃、CH₄、Cl₂、CO₂、CH₂=CH₂，回答下列相关问题：

（1）只含极性键且属于非极性分子的有　 ____．

（2）具有正四面体结构的非极性分子有　 ____　．

（3）既含有极性键又含有非极性键的微粒是　 ____　，该微粒中含有　 ____　个σ键　 ____　个π键．

（4）NH₃在水中的溶解度 ____（填“大于”、“小于”或“等于”）CH₄在水中的溶解度，其原因是　 ____　（填序号）

A．NH₃分子和水分子均为极性分子           B．CH₄分子和水分子均为非极性分子

C．NH₃分子为极性分子，水分子为非极性分子  D．NH₃分子与水分子间可形成氢键

阅读理解

    What's your hobby? Reading，playing sports or going to the movies?Hassan has an interesting hobby．He likes collecting tropicalfish(收集热带鱼)! He keeps this hobby for 7 years．Now he is 14．There is a big aquarium(养鱼缸)in his room．It is from his parents for his 13th birthday．There are many fish in it．All of the fish are cute and beautiful．

    Hassan often travels around the world(周游世界)with his family．He loves it because he can see the underwater world in many places．He always loves the colorful underwater world．Under the water,he can see lots of tropical fish．Sometimes he can see sharks(鲨鱼)．He wants to keep one or two small sharks in an aquarium,but he can't do it at home．So Hassan goes to help in the zoo on the weekend．There he can see a lot of sharks and some other big fish．Hassan likes working in the zoo，because he can work with his favorite animals and leam more about them．

根据材料内容选择最佳答案。

如图①，在边长为1个单位长度的小正方形组成的网格中，△ABC的三个顶点均在格点上．

（I）求点P的轨迹C的方程；

（II）是否存在过点A的直线 $l$ 与轨迹C相交于E、F两点，满足 $S_{\Delta OEF}=2\sqrt{2}$ （O为坐标原点）．若存在，求出直线 $l$ 的方程；若不存在，请说明理由．