An isthmus is a narrow strip of land that connects two larger land masses and separates two bodies of water. It is like a bridge between two larger land areas. Option 2 accurately describes an isthmus by stating that it is a narrow strip of land that separates two water bodies. This explanation aligns with the common definition of an isthmus and provides a clear distinction from the other options. Option 1, stating that an isthmus is a water body separating two land masses, is incorrect because an isthmus is actually a strip of land, not a body of water. Option 3`s explanation of a deep penetration of a water body in land is also incorrect; this description is more typical of a bay or a gulf. Option 4, none of these, is not the correct answer because option 2 accurately describes an isthmus.