单项选择题 One of them threatened me with a knife（）the other bound and gagged me.

单项选择题 Among the following research methods，which one is cheaper and easier？（）

单项选择题 Suppose that 50 ice cream cones are demanded at a particular price.If the price of ice cream cones rises from that price by 4 percent，the number of ice cream cones demanded falls to 46.Using the midpoint approach to calculate the price elasticity of demand，it follows that the（）