牙龈经常出血是何种维生素缺乏的表现（）
A.维生素A
B.维生素B1
C.维生素C
D.维生素D
E.维生素E
参考答案：C
Read and write. 我行我秀！读一读，仿照例子写句子。
例: Tomorrow I am going to fly kites. → Tomorrow I will fly kites.
1. → I will walk to the zoo.
2. He is going to play the guitar. →
3. We are going to learn Chinese. →
4. → They will lie on the grass.
重力式挡土墙一般由哪几部分组成？
