A:细胞甲的同源染色体成对排列在细脃中央
B:细胞甲产生的子细胞染色体数目减半
C:联会发生在细胞乙,而不会发生在细胞甲
D:细胞乙的染色体与亲代体细胞染色体数目相同
—Nero is crying. Do you know _______ she's so upset?
—Well, she lost her pet cat which was just like her family member.
昼夜更替产生的原因是( )