单项选择题 According to the author, economists were confused because（） .

单项选择题 According to the passage, which of the following strategies is NOT used by skilled learners（）

单项选择题 The expression“thrown off” in the third paragraph is closest in meaning to“（） ”.

单项选择题 Which of the following statements about Vandergrift’s research is TRUE（）

单项选择题 What does Vandergrift’s research show（）