请根据句意或括号中的中文提示、英文释义，写出句中所缺单词，使句子通顺。

(每小题1分，共5分) 

小题1:We have a growing          (人口) and therefore we need more food.

小题2:We all know that life is not always          (平坦的).

小题3:As soon as I had made the final decision, I felt very          (calm and not worried).

小题4:How can you          (have enough money to buy something) such a large house?

小题5:I like black and red, but my favourite          is blue.

故宫中的前三殿和后三宫分别是指（）（）（）（）（）（）。