精装书封壳的组合结构是什么？
参考答案：
精装书封壳组合结构里层为书封壳硬纸板、中径纸板或中径纸，表层为软质材料。
《淮南子?原道训》记载：“鲧(禹的父亲)筑城以卫(护)君，造郭(外城)以居人，此城郭之始也。”这表明当时 [ ]
A．宗法制逐步形成
B．分封制雏形形成
C．夏朝疆域基本固定
D．国家机器雏形产生
— I’m really glad to see you back.. ______ your trip to the valley interesting?
— No. it ______ very heavily there the whole time.
A．Was; was raining
B．Is; had rained
C．Was; was to rain
D．Is; has been raining
