单项选择题
A. They connect invisible phenomena to those we are familiar with. B. Scientists could not experiment without them. C. They give the scientist a sense of security. D. They provide deeper insight into the workings of the human mind.
A. in Europe in the eighteenth century B. in ancient Egypt and Babylon C. in the Far East in ancient times D. during the Middle Ages
A. he was quite sure of success B. he was not sure he would get the umbrella back C. he was rich enough to afford a new umbrella D. he did not know what to do