Many important inventions are the result of ______; for example, Chinese alchemists accidentally discovered gunpowder while trying to create an elixir that would make their emperor immortality.

(单选题)My mother was seriously ill last month. Luckily, she managed (单选题)There are three girls in the room, ______ is Tom’s sister. (单选题)It is reported that heavy coffee drinking and heart attack i (单选题)—Shall I tell John about it?—No, you ______. I’ve told him a (单选题)The assistant charged me 100 dollars for the blouse, but my (单选题)No one has finished his homework, ______? (单选题)The manager had fallen asleep where he ______, without undre (单选题)Where would this passage most probably appear? (单选题)What does the underlined word “alternative” mean in Chinese? (单选题)Why does the fourth paragraph take Space Science in context