Lenticels are used to help with gas exchange in woody stems--they are like snorkel valves on the outside of the stem. A tuber in wet soil would similarly be helped to exchange gas (such as waste carbon dioxide) by a lenticel.
Work Step by Step
Look in the text to see what lenticels are normally know for doing, and try to see how this could also be helpful in wet soil. Thinking about a snorkel is a useful analogy.