Dolly is a middle school girl. Her parents want to take her to Ice and Snow Festival. How much will they pay for the tickets?
A:¥20.
B:¥30.
C:¥50
D:¥60
与两栖动物相比,鸟类在生殖与发育方面较为进化的表现是( )
①体内受精
②体外受精
③卵生
④卵外有卵壳保护
⑤胎生
⑥亲鸟大多有孵卵、育雏等行为
①加清水 ②制作装片 ③观察质壁分离
④加0.3g•mL﹣1蔗糖溶液 ⑤观察质壁分离复原 ⑥观察正常细胞.