Bill: Hello, is that Dad?

Dad: Yes，it's me. How's your holiday? Are you having a good time in Sanya?

Bill: Yes. I'm collecting shells on the ____now. Where are you, Dad?

Dad: I am in the ____. I am ____a book.

Bill: Is Sally ____TV in the living room?

Dad: No. She is writing a ____in her bedroom.

Bill: OK. Miss you, Dad. Bye.

Dad: Bye.

少年儿童长期不注意坐、立、行的正确姿势，容易引起骨骼变形。其原因是：（  ）

窑洞是黄土高原地区最受欢迎的民居形式，与此有关的因素有（    ）

①占地少，建造成本低，适合当地的气候条件  ②黄土具有直立性，不易塌陷 ③窑洞是最坚固耐用的民居④窑洞隔音、隔热、保暖效果好