公安机关及其人民警察牢记全心全意为人民服务宗旨的要求是( )。

A．要真正把人民群众当做国家的主人，事事为群众着想
B．要勤政廉洁，秉公执法；乐于奉献，不怕艰难困苦，不怕流血牺牲
C．关心群众疾苦，开展便民、利民、助民活动，为群众排忧解难
D．自觉接受群众监督，坚持杜绝耍特权、逞威风、摆架子，破坏警民关系等违法乱纪的行为

--- My son is lost. Did you see a boy pass by here?

--- I saw ______ boy hidden behind ______ tree over there. You may go and have a look.

A．a; the

B．不填；the　

C．a; 不填　

D．a; a