Maven managed dependencies can not find the reasons and solutions for maven management dependencies

Figure one

Figure II
After selecting maven managed dependencies Figure II where a is not shown in FIG.

Reason: The project is not a maven project.
Solution 1: Rebuild a maven project with ecplise, then import your code into the new project, and run ok.
Solution 2: Add maven support. As shown below: select "Enable Dependency Management"

If it becomes the following figure, it means it is a maven project, and the problem is solved! .

PS: I used the second method.