- Has David finished his project yet?
- I guess not. He ___________ on it at lunch time. Do you want me to confirm it?
A:is working
B:was working
C:has worked
D:had worked
《荀子·儒效篇》载:“(周公)兼制天下,立七十一国,姬姓独居五十三人。”这说明西周分封制度的主体是( )