单项选择题
If you want this painkiller, you'll have to ask the doctor for a （）
A．transaction B．permit C．settlement D．prescription
单项选择题 The passage tells us that proof of life on Mars would （）
单项选择题 By saying "With Mars the scientific stakes are arguably higher than they have ever been" ( Line 1, Para. 4 ), the author means that （）
单项选择题 What is the main goal of sending human missions to Mars（）
