2. The biologist injected
coloring matter into anatomical specimens for the study of the structure.

那位生物学家往解剖标本中注入有色物质以供结构研究。
3. The construction of edge covered critical graphs is an important problem in the edge cover-
coloring of graphs.

在图的边覆盖染色中边覆盖临界图的构造问题一直是研究的热点和难题。