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（）

判断题 Phonology studies the description and classification of speech sounds.（）