根据首字母提示填写单词所缺部分，使句子完整。
小题1:There’s nothing in the bottle. It’s e____________.
小题2:Please k_________at the door before coming into the room.
小题3:At the beginning of 18th c_________, the population of the world was very small.
小题4:I’m very h_______. Please give me something to eat.
小题5:Mary looks unhappy. Let's have a try to c_________her up.
