单项选择题
A. Scientists consider apes may drive trains some day. B. Apes have worked in some factories. C. Apes may one day be used to gather crops. D. An ape is not a large monkey.
A. Black stands for unhappiness. B. Black makes people think of night. C. Black makes people think of sorrow. D. Black is the color of the mourning.
A. Just in case someone asks. B. Scientists like to take tests. C. Scientists are not very busy. D. To keep track of pollution levels.