Sue: Hello, I want to buy some ping­pong balls. Can you help me?

Clerk: Sure. Do you like these balls or those balls?

Sue: I like these balls. How much are they?

Clerk: They're 2 dollars each.

Sue: I need three ping­pong balls.

Clerk: OK. Here they are.

Sue: Thank you.

Clerk: You're welcome.

如图，在三棱锥P﹣ABC中，E，F分别为AC，BC的中点．

（1）求证：EF∥平面PAB；

（2）若平面PAC⊥平面ABC，且PA=PC，∠ABC=90°，求证：平面PEF⊥平面PBC．

打工妹小玉这样描述自己的家乡：“风光秀美，有许多热带雨林植物，独特的傣族文化，是全国著名的旅游区。”据此可判断小玉的家乡可能位于