1.) Roll back testing is done to see if the old code (after the new code is tested and un-installed) works as expected. Not heard of roll forward testing - probably opposite to the above statement.
2.) Requirement traceability matrix contains many to many relationship between the requirements of a project and the test cases created based on these requirements. This gives the tester and the management about the coverage of the test cases - whether it covers all the requirements. This also unreveals missed requirements.
3.) Junior QA uses QC at the greatest extent, mostly in writing test cases, managing results, test lab management, creating defects, assigning defects, tracking defects, linking defects to test cases etc.
Hope this helps.

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