俗话说：“人是铁，饭是钢，一顿不吃饿得慌．”这句话形象地说明了生物的生存需要（　　）

A．阳光

B．充足的空气

C．适宜的温度

D．营养物质

对话填词。

A: What's this?

B: It's a photo 1_______ my sister.

A: You have a nice sister.

B: Thanks.

A: Where 2_______ your sister work?

B: She 3_______ at a hospital.

A: What 4_______ she do?

B: She is a doctor. What 5_______ your sister?

A: She is a doctor, 6_______.

B: Does she like the job?

A: No. she 7_______ it's difficult.

B: What does she want to 8_______?

A: Sorry, I don't know.