泪膜
参考答案：
泪膜是指通过瞬目运动、涂布在眼表的一超薄层泪液膜。
______ he is five years old, ______ he swims as well as his father. [ ]
A. Because, so
B. Because, /
C. Though, but
D. Though, /
未经化学处理的森林凋落物
