有学者指出：“古来帝王，由秦始皇至清代宣统，正统偏安者共二百余人，真正懂得国家政体并善以此治国，王而不藩者，不过秦皇、汉武、宋太祖、清圣祖（康熙）四人而已。”这里的“国家政体”是指（    ）

为了在四位学生中选拔一名参加数学竞赛，目标是争取获奖，因此对他们的数学成绩分析后得出：四位学生的平均成绩均为96分，甲同学的成绩方差为0.54；乙同学的成绩方差为0.44；丙同学的成绩方差为0.45；丁同学的成绩方差为0.53。则应该选（   ）参加比赛比较稳。      

    Today is Saturday. The weather is warm and sunny. Bob and Jack go to the park. There are many people there. The girl under a big tree is reading a book. Two boys are playing football on the grass. The girl in a red dress is riding a bike. Two women are talking. The man beside these women is playing with a baby. Bob and Jack are beside the river. They are sitting on the chair and drawing pictures.

⑴It's warm and sunny ____       A. are beside the river.

⑵There are many people ____    B. are talking.

⑶Two boys ____                 C. in the park.

⑷Two women ____              D. are playing football on the grass.

⑸Bob and Jack ____             E. on Saturday.