An isthmmus is defined as a narrow strip of land connecting two larger land areas, typically separating two bodies of water. Classic examples include the Isthmus of Panama (connecting North and South America) and the Isthmus of Suez (connecting Africa and Asia). This geographical feature is significant for both natural ecosystems and human transportation routes like canals. Option B has a typo ('tow' instead of 'two') but is conceptually correct.