Google Collections has been deprecated and moved into Guava. Exclude it from A. With Maven, you do that with the exclusions tag below the dependency tag in your project's POM:
<dependency>
<groupId>org.project</groupId>
<artifactId>library-a</artifactId>
<version>[version]</version>
<exclusions>
<exclusion>
<!-- whatever the correct values are -->
<artifactId>google-collections</artifactId>
<groupId>google-collections</groupId>
</exclusion>
</exclusions>
</dependency>