汉语拼音的学习干扰英语音标的学习，叫做（）迁移。
参考答案：负
商品堆码时，货棚内或露天堆码都应排水畅通，地势高于周围地面，堆垛时要垫高（）。
A.20-30cm
B.15-20cm
C.30-40cm
D.40-50cm
一Is this your bicycle, David?
一No, it's not_____. It's Helen's. [ ]
A. his
B. yours
C. mine
D. hers
