1. Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back. 大家都知道，在墙壁或山腰附近发出的喊声，就会听到回声。
2. But scientists are working hard to turn them into realities. 但是, 科学家们正在努力工作, 以便把想法变成现实.
3. Before returning home at night, he took a shower and changed back into his suit. 晚上回家前,他洗个淋浴,又换上他那套西装.
4. Because of this, we kept looking back, wondering if we were leaving a trail of oil and petrol behind us. 因此，我们不时地掉过头，怀疑车后是否留下了机油和汽油的痕迹。
5. Before we had time to worry about what might happen, we were back on the plain again. 我们还未来得及担心后果，车已重新开上了平地。
6. Before returning home at night, he took a shower and changed back into his suit. 晚上回家前，他洗个淋浴，重新换上那身黑色西服。
7. By January 10th, I was back to where I had started from. 到了1月10日，我恢复了原来的作息时间。
8. Back in the train, we told each other what a wonderful time we had had that day. 回去的火车上，大家都说，这一天过得真愉快。
9. But I am going to buy them all back again now!" 不过现在我要把这些东西一一买回来。”
10. Back in the early 1960s, when the laser was first being developed, it was viewed by some as a fascinating research tool, others called it a science-fiction toy. 追溯到二十世纪六十年代初期,当激光最初被开发利用时，一些人视之为神奇的科研工具，另一些人则称之为科幻小说里的玩具。