C：C2H4 C3H4
A：CH4 C2H4
B：CH4 C3H6
D：CH4 C3H4
Christmas is my favourite 1. On Christmas, my family 2 my aunt，uncle and cousin to our house. We 3 gifts to each other. I give my cousin a 4 gift. We sing the Christmas 5 together. I think we are very happy.
简述观察叶片的结构实验的一般步骤？
下列各组词语中划线字的书写或注音有误的一项是（ ）
