  Theory of extensions of Hilbert C*-modules was developed by D. Bakic and B.
Guljas. An easy observation shows that in the case, when the underlying
C*-algebra extension is commutative and the Hilbert C*-modules are projective
of finite type, the algebraic properties of the corresponding Busby invariant
allow to identify extensions with isometric maps of the corresponding vector
bundles. When the Hilbert C*-modules are free of rank one, we evaluate the set
of extensions in topological terms.
