P 38, exercise 3: 在 P38 练习2中,提到了三个案例(case study 1, case study 2, case study 3), 本练习中的7句评论,分别说的哪个案例, 把序号(1, 2, 3)填入空格处。 Attention: number only Which case study does each comment refer to? fill out the blank with 1, 2 or 3, which is a short term for case study 1, case study 2, case study 3.