— is it from your home to your school?
— It is about twenty minutes by bike.
A:How far
B:How long
C:How many
D:How much
人体的呼吸系统是由____和____组成的.
油菜物种Ⅰ(2n=20)与Ⅱ(2n=18)杂交产生的幼苗经秋水仙素处理后,得到一个油菜新品系(注:Ⅰ的染色体和Ⅱ的染色体在减数分裂不会相互配对)