从所给出的句子中选出合适的完成对话。

A. What is your Grandpa doing?  B. Is your mother cooking? C. Are you having a good time in Sanya? D. She is painting a picture. E. I'm in the living room.

Dad: Hi, is that Betty?

Betty: Yes, it's me，Dad. How's your holiday? 

Dad: Yes, I am. I am at the beach now. Where are you, Betty?

Betty:

Dad:

Betty: Yes, she is cooking dinner in the kitchen.

Dad:

Betty: He is reading a book.

Dad: How about your Grandma? What is she doing?

Betty: She's good at painting.