  We prove that any vector field on a three-dimensional compact manifold can be
approximated in the C1-topology by one which is singular hyperbolic or by one
which exhibits a homoclinic tangency associated to a regular hyperbolic
periodic orbit. This answers a conjecture by Palis.
  During the proof we obtain several other results with independent interest: a
compactification of the rescaled sectional Poincar\'e flow and a generalization
of Ma\~n\'e-Pujals-Sambarino theorem for three-dimensional C2 vector fields
with singularities.
